Frequency agile broadband communications system

ABSTRACT

A broadband communications system for coupling telephony or other digital networks to a CATV network. The system transmits a multiplex of telephony signals in the forward band of the CATV network. Each forward channel is QPR modulated on a carrier and contains multiple subscriber telephony signals. The forward telephony channels are demodulated and demultiplexed by a plurality of subscriber terminals into the individual telephony signals directed to an addressed subscriber. Audio and control signals returning from the subscriber are digitized into standard telephony signals and QPSK modulated on a carrier onto the reverse band of the CATV network. The multiplicity of reverse band telephony channels are demodulated and multiplexed into a standard telephony signal which is directly interfaced to the telephony network. The reverse band modulators are frequency agile and modulate telephony signals from a subscriber in a selected one or more frequency subbands in the reverse band of the subscription network, so as to provide selectably changeable frequencies and selectably variable bandwidth in the reverse band commensurate with a selected subscriber communication feature. e.g. a single voice line, multiple voice lines, ISDN service, data communications services, security monitoring services, etc.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of application Ser. No.08/123,363, filed Sep. 17, 1993, now U.S. Pat. No. 5,499,241, entitled"Broadband Communications System".

FIELD OF THE INVENTION

The system pertains generally to broadband communications systems, suchas cable or community antenna television (CATV) networks, and is moreparticularly directed to communicating telephony signals, and other orsimilar signals, over CATV and equivalent networks.

BACKGROUND OF THE INVENTION

In order to introduce the present invention and the problems that itsolves, it is useful to overview a conventional CATV broadbandcommunication system, and then examine certain prior approaches toproblems encountered when attempting to introduce telephony signals intothe broadband environment.

Conventional Cable Television Systems (CATV)

Cable television systems, sometimes referred to as community-antennatelevision (CATV) systems, are broadband communications networks ofcoaxial cable and optical fiber that distribute television, audio, anddata signals to subscriber homes or businesses. In a typical CATVsystem, a single advantageously located antenna array feeding a cablenetwork supplies each individual subscriber with a usable televisionsignal.

Since the pioneer days, cable networks have experienced enormous growthand expansion in the United States, particularly in urban networks. Itis estimated that CATV networks currently pass approximately 90% of thepopulation in the United States, with approximately 60-65% of allhouseholds actually being connected. While cable systems originally hadvery simple architectures and provided a limited number of differenttelevision signals, the increase in the number of televisionbroadcasters and television owners over the last several decades hasresulted in much more complex and costly modern cable distributionsystems.

A typical CATV system comprises four main elements: a headend, a trunksystem, a distribution system, and subscriber drops.

The "headend" is a signal reception and processing center that collects,organizes and distributes signals. The headend receivessatellite-delivered video and audio programming, over-the-air broadcastTV station signals, and network feeds delivered by terrestrial microwaveand other communication systems. In addition, headends may inject localbroadcasting into the package of signals sent to subscribers such ascommercials and live programming created in a studio.

The headend contains signal-processing equipment that controls theoutput level of the signals, regulates the signal-to-noise ratio, andsuppresses undesired out-of-band signals. Typical signal-processingequipment includes a heterodyne processor or a demodulator-modulatorpair. The headend then modulates received signals onto separate radiofrequency (RF) carriers and combines them for transmission over thecable system.

The "trunk system" is the main artery of the CATV network that carriesthe signals from the headend to a number of distribution points in thecommunity. A modern trunk system typically comprises of a combination ofcoaxial cable and optical fibers with trunk amplifiers periodicallyspaced to compensate for attenuation of the signals along the line. Suchmodern trunk systems utilizing fiber optics and coaxial cable are oftenreferred to as "fiber/coax" systems.

The "distribution systems" utilize a combination of optical fibers andcoaxial cable to deliver signals from the trunk system into individualneighborhoods for distribution to subscribers. In order to compensatefor various losses and distortions inherent in the transmission ofsignals along the cable network, line-extender amplifiers are placed atcertain intervals along the length of the cable. Each amplifier is givenjust enough gain to overcome the attenuation loss of the section of thecable that precedes it. A distribution network is also called the"feeder".

There is a strong desire in the CATV and telecommunications industry topush optical fiber as deeply as possible into communities, since opticalfiber communications can carry more signals than conventional networks.Due to technological and economic limitations, it has not yet provedfeasible to provide fiber to the subscriber's home. Present day "fiberdeep" CATV distribution systems including optical fibers and coaxialcable are often called "fiber-To-the-Serving-Area" or "FFSA" systems.

"Subscriber drops" are taps in the distribution system that feedindividual 75 Ω coaxial cable lines into subscribers' television sets orsubscriber terminals, often referred to as "subscriber premisesequipment" or "customer premises equipment" ("CPE"). Since the tap isthe final service point immediately prior to the subscriber premises,channel authorization circuitry is often placed in the tap to controlaccess to scrambled or premium programming.

Cable distribution systems were originally designed to distributetelevision and radio signals in the "downstream" direction only (i.e.,from a central headend location to multiple subscriber locations, alsoreferred to as the "forward" path). Therefore, the component equipmentof many older cable systems, which includes amplifiers and compensationnetworks, is typically adapted to deliver signals in the forwarddirection only. For downstream transmissions, typical CATV systemsprovide a series of video channels, each 6 MHz in bandwidth, which arefrequency division multiplexed across the forward band, in the 50 MHz to550 MHz region of the frequency spectrum. As fiber is moved more deeplyinto the serving areas in fiber/coax and FTSA configurations, thebandwidth of the coax portion is expected to increase to over 1 GHz.

The advent of pay-per-view services and other interactive televisionapplications has fueled the development of bidirectional or "two-way"cable systems that also provide for the transmission of signals from thesubscriber locations back to the headend. This is often referred to asthe "upstream" direction or the "reverse" path. This technology hasallowed cable operators to provide many new interactive subscriberservices on the network, such as impulse-pay-per-view (IPPV). In manyCATV systems, the band of signals from 5 MHz to 30 MHz is used forreverse path signals.

However, the topology of a typical CATV system, which looks like a "treeand branch" with the headend at the base and branching outwardly to thesubscriber's, creates technical difficulties in transmitting signals inthe upstream direction back to the headend. In the traditional tree andbranch cable network, a common set of downstream signals are distributedto every subscriber home in the network. Upstream signals flowing from asingle subscriber toward the headend pass by all the other upstreamsubscriber homes on the segment of distribution cable that serves theneighborhood.

The standard tree and branch topology has not proven to be well suitedfor sending signals from each subscriber location back to the headend,as is required for bidirectional communication services. Tree and branchcable distribution systems are the most efficient in terms of cable anddistribution usage when signals have to be distributed in only thedownstream direction. A cable distribution system is generally a verynoisy environment, especially in the reverse path. Interfering signalsmay originate from a number of common sources, such as airplanes passingoverhead or from Citizens Band (CB) radios that operate at a commonfrequency of 27 MHz, which is within the typical reverse channelbandwidth of CATV networks. Since the reverse direction of a tree andbranch configuration appears as an inverted tree, noise is propagatedfrom multiple distribution points to a single point, the headend.Therefore, all of the individual noise contributions collectively addtogether to produce a very noisy environment and a communicationsproblem at the headend.

Present day FTSA systems facilitate the communication of signals in thereverse direction by dividing the subscriber base of a cable networkinto manageable serving areas of approximately 400-2500 subscribers.This allows for the reuse of limited reverse band frequency ranges forsmaller groups of subscribers. The headend serves as the central hub ofa star configuration to which each serving area is coupled by an opticalcommunications path ending in a fiber node. The fiber node is connectedto the serving area subscribers over a coaxial cable distributionsub-network of feeders and drops in each serving area. In the FTSAconfiguration, some of the signals in the forward direction (e.g.,television program signals) are identical for each serving area so thatthe same subscriber service is provided to all subscribers. In thereverse direction, the configuration provides an independent spectrum offrequencies confined to the particular serving area. The FTSAarchitecture thus provides the advantage of multiplying the bandwidth ofthe reverse portions of the frequency spectrum times the number ofserving areas.

The Desire for Telephony Service

The ever-expanding deployment of fiber optic technology in CATV systemsacross the country has cable operators looking to provide a whole newrange of interactive services on the cable network. One area that is ofparticular interest is telephony service. Because of recent advances intechnology as well as the loosening of regulations, the once distinctlines between the cable television network and the telephone networkhave blurred considerably. Currently there is a great demand for abroadband communication system that can efficiently provide telephoneservice over the existing cable distribution network.

Moreover, there is substantial interest expressed by telephone systemoperating companies in the idea of increased bandwidth for provision ofnew services to telephone subscribers, such as television; interactivecomputing, shopping, and entertainment; videoconferencing, etc. Presentday "copper" based telephony service (so called because of the use ofcopper wires for telephone lines) is very bandwidth limited--about 3kHz--and cannot provide for such enhanced services by the telephonecompanies without massive changes to the telephone networksinfrastructure.

Existing communications systems, however, have not proven to be wellsuited for the transmission of telephony signals on the cable network. Asystem for transmitting telephony signals must be configured to allowsingle point to single point distribution (i.e., from a singlesubscriber to a single subscriber). However, unlike the telephonecompanies with their well-established national two-way networks, thecable industry is fragmented into thousands of individual systems thatare generally incapable of communicating with one another. The cablenetwork is instead ideally configured for single point to multiple pointsignal transmission (i.e., from a single headend downstream to multiplesubscriber locations).

Moreover, CATV systems do not have the switching capabilities necessaryto provide point to point communications. A communications system forthe transmission of telephone signals must therefore be compatible withthe public switched telephone networks ("PSTN") operated by thetelephone operating companies. To be useful in the carriage of telephonysignals, a CATV network must be able to seamlessly interface to atelephony network at a point where it is commercially viable to carrytelephony signals. It must also provide signals that can pass to otherparts of the interconnected telephone systems without extensivemodulation or protocol changes to thereby become part of theinternational telephone system.

Telephony on Data Communications Network

One approach taken to provide a bidirectional broadband communicationssystem is shown in U.S. Pat. No. 5,084,903 of McNamara et al., assignedto First Pacific Networks (hereinafter referred to as "FPN"). Thispatent describes an approach to the communication of telephony signalsthat appears primarily designed to operate in an office-type datacommunications network environment (e.g., Ethernet). Data communicationsnetworks are typically bandwidth symmetrical, that is, the forward andreverse signal paths consume equal amounts of bandwidth, and thetopology is star or serial, not tree and branch. In contrast, CATVnetworks are bandwidth asymmetrical, with heavy allocation of bandwidthfor use in the downstream direction and limited upstream bandwidth. Asthe present inventors have discovered, the noise problem in the upstreamdirection is difficult in a broadband bandwidth-asymmetrical, tree andbranch topology, as contrasted with a symmetrical office-type datacommunications network.

The system described in the FPN patent employs two different modulationschemes for communicating information between a central headend and aplurality of subscriber nodes. For downstream communications, the FPNsystem transmits signals continuously in a plurality of 6 MHz bandwidthchannels. In a preferred embodiment, an AM-PSK modulator is used in thedownstream path. For upstream communications, the FPN system transmitspackets of information in bursts to a headend using an offset quadraturephase shift keyed (OQPSK) modulator.

While the FPN communications system may be suitable for communicatingtelephony signals on a data communications network such as Ethernet, itdoes not solve certain problems that occur in the carriage of telephonysignals on a broadband cable network. Due to the single point tomultiple point configuration (tree and branch) of the CATV network,upstream transmissions of telephony signals have to contend withmultiple noise sources as the branch signals from each subscriber aremerged together toward the headend. It is believed, however, that theburst mode approach used in the reverse path of the FPN system isparticularly susceptible to these noise issues. Specifically, it isbelieved that the framing bits and sequencing of the data streams aresusceptible to interruption when an interference signal is sustained forany significant length of time (i.e., for longer than the length of adata frame) anywhere within one of the 6 MHz bandwidth channels used tocarry telephony signals.

It is further believed that the interruption of the framing bits mayresult in the loss of content in all telephone conversations representedwithin the data frame interrupted. In a data communications environment,this signal interruption may only be noticeable as a slowdown on thenetwork, and, though inconvenient, may be considered acceptable.However, such degradation of signal quality in a cable and telephonyenvironment is undesirable and may be unacceptable.

There is no discussion in the FPN patent of any means for insertion orremoval of telephony signals from and to the public switched telephonenetwork (PSTN). The FPN system appears to provide only a local areatelephone network designed primarily for inter-office communications(such as office to office intercom), as only limited access to the PSTNis suggested. There are a number of different locations in the FPNequipment where telephony signal insertion and removal could occur, butthe patent does not describe any means for signal insertion or removal,or discuss any of the issues associated with signal insertion andremoval. At best, it appears that telephony signals would be insertedand removed at nodes directly connected to the broadband media (e.g.,the coaxial cable), as suggested at col. 3, line 30. The patent does notindicate how such insertion and removal directly from the broadbandmedium should best be effected, and is silent on issues involvingmultiple telephony channels.

Therefore, there is a need for a broadband communications system that iscompatible with the existing public switched telephone networks and thatis not sensitive to noise or other interference issues, particularly inthe reverse path. There is also a need for a broadband communicationssystem that is bandwidth efficient and provides a higher spectralefficiency than present systems, thereby increasing the number ofsubscribers that may be served by each broadband network with telephonyand enhanced services offered by CATV system operators, telephonecompany operating companies, and others.

SUMMARY OF THE INVENTION

The invention includes methods and apparatus for providing broadbandcommunications, including bidirectional telephony communications, over acable distribution network. In particular, the present inventionprovides an integrated CATV/telephony system that is compatible withtoday's public switched telephone networks and can also deliver video,data, security monitoring, and other services without affecting currentin-home wiring or equipment.

In one embodiment, the method includes communicating telephony signalsfrom a telephony network to the CATV subscribers in the forward band ofthe cable network and communicating telephony signals from the CATVsubscribers to the telephony network in the reverse band of the cablenetwork.

In another preferred embodiment, the method includes the digitizing ofindividual subscriber telephony signals into a multiplexed signal thatis carried on a frequency division multiplexed (FDM) carrier in theforward band of the cable network. The digital multiplexed signal isquadrature partial response (QPR) modulated on a carrier which ispositioned in an otherwise unused portion of the CATV network forwardband. In the illustrated embodiment, the QPR signal is preferablyapproximately 3 MHz in bandwidth and easily fits in a standard 6 MHzvideo channel. In another preferred embodiment, a pair of the QPRsignals can be placed in an otherwise unused channel in the cable lineto utilize approximately 6 MHz of bandwidth. By making a system whichuses a robust digital signal, the bandwidth of the forward CATV band canbe efficiently allocated. The system operator can plan and change theseallocations on a flexible basis as new services are made available orold services are taken off line.

In a preferred embodiment, the subscriber telephony signals to thetelephony network are digitized and individually modulated on a carrierin the reverse band of the CATV system. As an illustrated example, asubscriber DS0 telephony line is QPSK modulated into a 50 kHz bandwidthsignal and frequency division multiplexed on the reverse band of theCATV network. The individual telephony signals are multiplexed into astandard time-division multiplexed (TDM) telephony signal which can beadapted to couple directly into a SONET port or other standard telephonyconnection, such as a DS1, DS2, or DS3 format signal, of the telephonynetwork.

By using the reverse band of the CATV network in small increments of 50kHz, the flexibility of the reverse signaling band is not compromised.The system operator can still provide interactive TV services, IPPVservices, and other reverse path signals while providing telephonyservice.

The number of subscribers served by the telephony service can beincreased several fold if the CATV network is a FTSA network. The space(frequency) division multiplexing (FDM) used in the reverse band makesit economical to provide a substantial number subscribers in a servingarea with a telephony service. If a serving area contains 500subscribers, then the bandwidth needed for a dual path system at 50 kHzper subscriber would be 25 MHz, within the 5-30 MHz reverse band of themost prevalent split band systems.

According to another aspect of the invention, the reverse band circuitryis frequency agile, and is responsive to channel information provided ina directory channel in the forward band from the headend interface unitfor tuning to one or more selected reverse band frequencies, formodulating the telephony signals from the customer interface unit in theone or more selected frequency subbands. The frequency agile featurepermits the selective allocation of bandwidth to satisfy subscriberdemands and change reverse band channels in response to noise in achannel. The frequency agility permits the invention to carry outdynamic bandwidth allocation to effect varying levels of service forsubscribers, e.g. single voice line, multiple voice line, ISDN, datacommunications, etc., and avoid particular reverse band channels thatare susceptible to and/or are experiencing noise.

According to another aspect of the invention, the system is operative todetermine an appropriate service level to provide communications to aparticular subscriber, and allocate one or more selected frequencysubbands in the reverse band of the subscription network so as toprovide selectably variable bandwidth commensurate with the determinedappropriate service level. The identity of the one or more selectedfrequency subbands are communicated to the particular subscriber in adirectory channel in a forward band. Incoming telephony signals arecommunicated to the particular subscriber in the forward band offrequencies, as in other embodiments of the invention. At the subscriberterminal associated with the particular subscriber, the identity of theone or more selected frequency subbands for communications back to theheadend is received via monitoring the directory channel. Subscribertelephony signals are then communicated to the headend in the one ormore selected frequency reverse frequency subbands.

In the alternative frequency agile embodiment, a pair of subscriber DS0telephony lines are QPSK modulated into a 108 kHz bandwidth signal, with20 kHz guard band, and frequency division multiplexed on the reverseband of the CATV network. In this embodiment, there is capacity forhandling 388 DS0 equivalent telephony channels in the 5 MHz to 30 MHzreverse band. To serve 388 subscribers with a single DS0 telephonyservice, then the bandwidth needed for a dual path system is as follows:194 downstream channels, each channel carrying 2 DS0's, each channel at128 kHz, yielding about 25 MHz, positioned within the 5-30 MHz reverseband of the most prevalent split band systems.

Access to the broadband communications system is provided by aresidential interface unit, also called a "customer interface unit"(CIU), installed outside the subscriber's premises. The broadbandtelephone signals are terminated at the end of the CATV drop cable andpass through the home as a standard two-wire telephone signal. Thesubscriber's interior telephony network can disconnected from thetelephone company copper network and connected or jumpered directly tothe CIU.

The particular modulation technique utilized in the downstream pathresults in increased spectral efficiency of the communications systemover traditional approaches. For the preferred embodiment utilizing 194dual-DS0 upstream channels at 128 kHz per channel, the spectralefficiency is as follows:

    efficiency=(388 DS0's×64 kbps/DS0)/25 MHz=1 bit per Hz

As described, one of the primary advantages of the present invention isits frequency agility, and the ability to allocate bandwidth tosubscribers on demand. The frequency agile feature is preferablyprovided in the reverse band of the communications system, and isoperative for modulating a telephony signal from a subscriber in one ormore frequency subbands in the reverse band of the subscription networkso as to provide selectably variable bandwidth in the second bandcommensurate with selected subscriber communication features. Forexample, a subscriber can subscribe to a single voice grade linetelephone service, plural voice grade telephone line service, ISDNtelephone service, local or wide area network communication services(e.g. ETHERNET, Appletalk), security monitoring communication services,or the like.

The present invention therefore differs from conventional systems byproviding dynamic frequency assignment, in which each subscriber isallocated bandwidth on demand. This approach provides the ability tochange the frequency if an interfering carrier is introduced during thecourse of a conversation.

According to yet another aspect of the invention, the preferred systemprovides each subscriber premises with a unique address that ispermanently configured in the CIU such as a FLASH ROM or PROM. Thisallows the headend of the cable system to communicate with each CIUindividually. When a subscriber communicates with the headend to requesttelephony service, the headend can verify the levels of subscriberservice or features that are authorized for the requesting subscriber,and appropriate bandwidth (e.g. DS0 channels) can be allocatedcommensurate with the authorized and requested level of service orfeature.

According to yet another aspect of the invention, the preferred systemalso provides for the ability to monitor or verify signal performance atany time.

The alternative embodiment carries out steps of monitoring the noiselevel in the 128 kHz subbands provided in the reverse spectrum, andchanging the frequency of a selected subband allocated for provision ofservice to a selected subscriber in response to a determination that thenoise level in the monitored subband exceeds a predetermined threshold.This permits dynamic reallocation of telephony signal from a particularregion in the reverse channel spectrum that may be subject to noise orinterference, so as to move the reverse band communication to a regionof the spectrum that is cleaner.

While each standard DS0 telephony voice channel typically has a 64 kbpsrequirement, the present system provides two 64 kbps DS0 voice channelsand one 16 kbps digital overhead channel, for a total of 144 kbps ofactual data per 128 kHz channel. The overhead channel carriesinformation including the identity of the caller, the calling party'sphone number, the called party's phone number, the switch position, andthe line position. The overhead information may also contain datacapability. For example, a bit error test in a loop back condition maybe sent in the extra bits during the conversation to evaluate the signalquality. If the signal quality falls below some predetermined threshold(to be determined by the user or the system), the system will change theupstream or downstream carrier.

A system constructed in accordance with the present invention providesthe further advantage of compatibility with a growing market. As cableoperators begin to provide telephony service over the cable network, itmay be desirable not to have to initially allocate the entire reversebandwidth for upstream telephony signals. Likewise, as telephonyapplications increase, it may be desirable to allocate more bandwidth totelephony applications than nominal 25 MHz provided in the disclosedembodiment. Ideally, the cable operators would like to deploy hardwareand modify architectures as the consumer demand dictates. Furthermore,there may be instances where a subscriber may have an application thathas a higher bandwidth requirement (e.g., video teleconferencing at 384kbps). Systems that assign a predetermined, unchangeable segment ofbandwidth to each subscriber, however, do not have the flexibility toexpand or selectably allocate bandwidth in response to demand. Instead,each subscriber must be provided with hardware established at a certainfrequency. The present invention, instead of assigning each subscriber adedicated frequency, allocates as many channels as needed in response todemands for a particular level of service. Thus, the present system canprovide subscribers with services such as video teleconferencing, faxlines, multiple voice lines, ISDN, etc. as needed.

These and other objects, features and advantages of the invention willbe better understood and more fully appreciated if a reading of thefollowing detailed description is undertaken in conjunction with theappended drawings and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a system block diagram of a broadband telephony systemconstructed in accordance with the invention.

FIG. 2 is a system block diagram of one embodiment of the broadbandcommunications system illustrated in FIG. 1 connected to a telephonynetwork.

FIG. 3A is a pictorial representation of the frequency allocation oftypical split CATV systems illustrating their forward and reversesignaling bands.

FIG. 3B is a pictorial representation of the frequency allocation of thebroadband communications system illustrated in FIG. 2.

FIG. 3C is a pictorial representation of the frequency allocation of analternative embodiment of the broadband communications system.

FIG. 4 is a detailed block diagram of the telephony network to the CATVnetwork input interface of the system illustrated in FIG. 2.

FIG. 5 is a detailed block diagram of the telephony network to the CATVnetwork output interface of the system illustrated in FIG. 2.

FIG. 6 is a detailed block diagram of a telephony terminal for receivingtelephony signals from the telephony network through the CATV networkand for transmitting telephony signals to the telephony network throughthe CATV network.

FIGS. 7A and 7B are detailed block diagrams of the DS1 to DS2multiplexer of the input interface illustrated in FIG. 4.

FIG. 8 is a detailed block diagram of a modulator for telephony terminalillustrated in FIG. 6.

FIG. 9A is a pictorial representation of the framing protocol of themodulator illustrated in FIG. 8.

FIG. 9B is a pictorial representation of the framing protocol or dataformat of the reverse path signals utilized in an alternative embodimentof the present invention.

FIG. 9C is a pictorial representation of the framing protocol or dataformat of the forward path signals utilized in an alternative embodimentof the present invention.

FIG. 10 is a detailed block diagram of the demodulator of thetuner/demodulator of the output interface illustrated in FIG. 5.

FIG. 11 is a block diagram of a headend interface unit (HIU) constructedin accordance with an alternative embodiment of the present invention.

FIG. 12 is a detailed block diagram of a customer interface unit (CIU)constructed in accordance with an alternative embodiment of the presentinvention.

FIG. 13 is a detailed block schematic diagram of the reverse modulatorutilized in the customer interface unit (CIU) illustrated in FIG. 12.

FIG. 14 is a detailed block schematic diagram of the reverse demodulatorconverter utilized in the headend unit (HIU) illustrated in FIG. 10.

FIG. 15 illustrates a service level table maintained by the headend unit(HIU) of FIG. 11 to allocate varying service levels requested bysubscribers with various reverse channel frequencies.

FIG. 16 illustrates the method carried out in the alternative HIU andCIU of FIGS. 11 and 12 for dynamic bandwidth allocation and frequencyassignment in the reverse channels.

FIG. 17 illustrates the method carried out in the alternative HIU andCIU of FIGS. 11 and 12 for handling a communication for a caller.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

With respect now to FIG. 1, there is shown a broadband communicationssystem constructed in accordance with the invention. The system will bedescribed in connection with the communications of telephony signals,but it will be evident that other signals of similar or equivalent typescan also be used. Further, while digital telephony signals aredescribed, the system is also capable of communicating analog telephonysignals or other types of digital signals. Telephony signals from thetelephony network are coupled to the CATV network 12 and arecommunicated over the CATV network to an addressed subscriber premises30. The addressed subscriber 30 communicates telephony signals back overthe CATV network 12 which are then coupled to the telephony network 10.The system serves as an extension of the telephony network 10 wheresubscribers can call out to the telephony network 10 or receive callsfrom the telephony network. This service is in addition to theconventional video, audio, data and other services provided to eachsubscriber by the CATV network 12.

By "headend", we do not mean to be limited to a conventional coaxialCATV headend such as 14, but also consider that an optical fiber nodesuch as 16 or other communication node that can serve the functions ofreceiving multiplexed communication signals from a source of signals,such as a telephony central office, and communicating such signals tosubscribers in the broadband network. As will be seen in the followingdiscussion, a CATV headend 16 is the preferred embodiment for effectingthese functions.

A preferred implementation of the broadband communications system isillustrated in FIG. 1. The system includes the telephony network 10which interfaces through an input interface 32 to the CATV network 12.The CATV network 12 further interfaces with the telephony network 10through an output interface 34. Telephony signals are communicated tosubscribers of the CATV network 12 through the input interface 32 to asubscriber premises 30. Telephony signals from the subscriber premises30 of the CATV network 12 are communicated over the CATV network 12 andthrough the output interface 34 to the telephony network 10. Thebroadband communications system does no switching and thus takesadvantage of the strength of the CATV network 12 for its broadbandcommunications path and the strength of the telephony network 10 for itsconnection and switching capability.

The CATV network 12 is illustrated as having a fiber to the serving area(FTSA) architecture. A headend 14 provides CATV programming which isdistributed via a distribution network to a plurality of subscribers attheir subscriber premises 30. The distribution network serves aplurality of "serving areas", such as the one referenced at 20, whichare groups of subscribers that are located proximate to one another.Each serving area is comprised of groups ranging in size from about 50homes to about 2500 homes. The headend 14 is coupled to each servingarea in a star configuration through an optical fiber 18 which ends in afiber node 16. The CATV programming and telephony signals are convertedfrom an RF broadband signal to light modulation at the headend 14,transmitted over the optical fiber 18, and then converted back to an RFbroadband signal at the fiber node 16. Radiating from each of the fibernodes 16 throughout its serving area 20 is a coaxial sub-network offeeders 22 having bidirectional amplifiers 24 and bidirectional lineextenders 25 for boosting the signal.

The RF broadband signal is distributed to each of the subscriberpremises 30 by tapping a portion of the signal from the nearest feeder22 with a tap 26, which is then connected to the subscriber premisesthrough a standard coaxial cable drop 28. The CATV network thus providesa broadband communications path from the headend 14 to each of thesubscriber premises 30, which can number in the several hundreds ofthousands.

While one preferred embodiment of the invention shows the inputinterface 32 coupled to the fiber node 16 and the output interface 34coupled to the headend 14, it is evident that the insertion andextraction of the RF telephony signals need not be limited to thissingle architecture. Both the input interface 32 and an output interface38 (shown in phantom) can be connected at the fiber node 16.Alternatively, both an input interface 36 (shown in phantom) and theoutput interface 34 can be coupled to the headend 14. Moreover, theinput interface 36 can be coupled to the headend 14, while the outputinterface 38 can be coupled to the fiber node 16. For cablearchitectures which do not conform to a star configuration, it isgenerally most advantageous to insert the RF telephony signals at theheadend and to extract them from the system at the headend. Eacharchitecture has its own distinct advantages as will be more fullydescribed hereinafter.

The input and output interfaces 32 and 34 produce a facile method forinserting the telephony signals in one direction and extracting thetelephony signals in the other. The telephony signals are transformedinto compatible RF signals which can be inserted or extracted from theCATV network 12 in much the same manner as other programming at variouspoints in the network. The compatibility of RF telephony signals withthe previous RF signals on the CATV network 12 allows their transmissionin a transparent manner over the network without interference to theother signals or special provision for their carriage.

Theoretically, the broadband communications path provided by the CATVnetwork 12 is bidirectional so that information can be passed in eachdirection. However, because of convention and the single point tomultipoint nature of most networks, the reverse path, i.e.,communications originating from the subscriber premises 30 andcommunicated to the headend 14, is much more limited. Normally, thereverse amplifiers 25 are bandwidth limited and include diplexers whichseparate the CATV spectrum into forward and reverse paths based onfrequency.

FIG. 2 illustrates a preferred implementation of the broadbandcommunication system configured as an extension to a telephony network.For connection to the telephony network 10, a class 5 switch 41 is used.The switch 41 has suitable circuitry for handling conventional local,trunk and interconnect signals which integrate the switch into the localarea, national and international calling grids. The switch 41 has aswitching network of crosspoints which may switch any of a plurality ofinputs to any plurality of outputs. Particularly, the switch 41 hasequipment to provide DS1 format interfaces.

As known to those skilled in the art, a "DS0" signal is a standardtelephony format corresponding to a 64 kb/s digital channel which can beused for voice, data, audio, etc. Thus a single DS0 telephony signal canbe viewed as a single telephone conversation. Likewise, a "DS1" signalcorresponds to a 1.544 Mb/s digital channel that contains 24 DS0channels. For a summary of the bit rates of the standard digitaltelephony formats and their relationships to one another, see TABLE 1below:

                  TABLE 1                                                         ______________________________________                                        Digital Signal                                                                            Bit Rate   DS0      DS1  DS3                                      ______________________________________                                        DS0         64 kb/s    1        1/24  1/672                                   DS1         1.544 Mb/s 24       1    1/28                                     (also T-1)                                                                    DS1C        3.152 Mb/s 48       2    1/14                                     DS2         6.312 Mb/s 96       4    1/7                                      DS3         44.736 Mb/s                                                                              672      28   1                                        OC-1        51.84 Mb/s 672      28   1                                        ______________________________________                                    

Additionally, the switch 41 has means for demultiplexing DS1 signalsinto a plurality of DS0 signals which then can be routed to outgoingpoints. The system uses a forward path which receives a plurality of theDS1 channels at the input interface 32 and connects them over the CATVnetwork 12 to the subscriber premises 30. The subscriber premises 30transmits telephony signals over the CATV network 12 to the outputinterface 34 which converts them back into the same number of DS1 signalchannels for transmission to the switch 41. If the switch 41 is locatedproximately to the input interface 32 and the output interface 34, thenthey can be coupled directly. Alternatively, as will be the mostprevalent case, where a headend or fiber node is not located proximatelyto the class 5 switch, an optical fiber link can be used to connect theswitch 41 and interfaces 32 and 34.

In the forward direction, a fiber optic transmitter 43 converts theplurality of DS1 telephony signals into an optical signal which istransmitted to a fiber optic receiver 45. The fiber optic receiver 45converts the optical signal back into the DS1 format telephony signals.Likewise, the fiber optic transmitter 49 in the reverse path convertsthe outgoing DS1 telephony signals into an optical signal which isreceived by the fiber optic receiver 47 for conversion back into the DS1telephony format signals.

The DS1 telephony signal format was chosen because it is a standardtelephony format, and conventional optical links to do the conversionand transmission are readily available for the transmitters 43, 49 andfor the optical receivers 45, 47.

The system uses this bidirectional mode of communication where each DS1signal contains 24 DS0 channels, which can be considered groups of 64kb/s digital data channels. The 64 kb/s channels can either be used forvoice, data, audio (music, stored information), etc. In general, fortelephony type signals, each DS0 channel derived from a connected DS1link is addressed to and associated with a particular subscriber. Thepreferred embodiment provides transport from each DS0 signal in theconnected DS1 link to the particular subscriber, by transmittingincoming telephony signals downstream in a selected DS0 downstreamchannel in the broadband system forward path, and has a correspondingDS0 upstream channel assigned to that subscriber in the broadband systemreverse path for outgoing telephony signals. Received DS0 signals fromsubscribers are then routed to the corresponding DS0 time slot in theDS1 link for outgoing signals. This permits the switch 41 to connect anyof the local, trunk or interconnect calling points to any of the DS0channels in the forward path and its associated DS0 channel in thereverse path to the same local, trunk or interconnect points forcompleting the communications path. Each of the subscribers 30 appearsas another DS0 subscriber connected directly to the class 5 switch 41.The distribution system of the CATV network 12 is transparent to theswitch 41 and does not need any further communication, information orconnection to the broadband communication system.

FIG. 3A illustrates a typical frequency allocation for many of theinstalled split band CATV networks. The frequencies used for programmingwhich generate the revenues for the system operator are carried in theforward band from 50 MHz to about 550 MHz. Although, the frequenciesabove 550 MHz are not presently used, there has been increased interestin providing additional services in this unused forward bandwidth,currently considered to extend to about 1 GHz. Conventionally, theforward band comprises a series of video channels, each 6 MHz inbandwidth, which are frequency division multiplexed across the forwardband. Several areas are not used and each video channel has a 1.5 MHzguard band between other adjacent channels.

In combination with the forward band, the typical CATV spectrum includesa reverse band from about 5-30 MHz. These frequencies have beenallocated for signals returning from the subscriber to the headend. Thisband has traditionally been relatively narrow because of the high noisefrom the funneling effects of the multiplicity of the multipoint signalsadding to a single point. Further, in the past bandwidth taken from theforward band has meant less revenues from other services. The presentinvention provides a solution to these problems by providing a systemwhere the telephony signals to a subscriber premises are communicated inthe forward band of the spectrum and the telephony signals from asubscriber premises are communicated in the reverse band of the CATVsystem.

As seen in FIG. 3B, the broadband communications system utilizes aplurality of frequency division multiplexed carriers in the forward bandto communicate the telephony signals to the subscribers. In theillustrated embodiment, five channels of approximately 3 MHz are used tocarry incoming telephony signals from the telephony network 10. Eachforward channel is a QPR modulated carrier, where the modulation occursas a 6.312 Mb/s digital data stream, specifically in a DS2 telephonysignal format including four DS1 telephony signals. The carriagecapacity of such a system is then 20 DS1 channels, or enough for 480 DS0voice channels.

Each of the reverse band signals are 50 kHz in bandwidth, which isnarrow enough to be easily placed at different frequency divisionmultiplexed positions in the frequency spectrum. The modulators arefrequency agile and can reallocate frequencies based upon traffic overthe system, noise, channel condition, and time of use. The 50 kHz widecarriers can be placed anywhere in the reverse band that there is spacefor them. Depending upon the CATV system, i.e., whether there is areverse amplification path in the distribution network, they could alsobe allocated to frequencies normally reserved for forward bandtransmissions. Further, such system is expandable by bandwidth for otheruses besides the individual telephony signals. For example, if aparticular subscriber required a return path of a greater bandwidth thanthe 50 kHz, then the bandwidth could be easily allocated to this usewithout a complete reconfiguration of the system. Such uses may includehigh speed data transmissions, trunk connections for small centraloffices, video services originating from the telephony network, andother uses requiring a nonstandard bandwidth.

There are a number of advantages with the broadband communicationssystem as described. It uses the reverse band efficiently and uses onlythat portion of the forward band which is necessary. Digital QPR andQPSK modulation is used to permit digital and telephony services to thesubscriber and provide a robust signaling method allowing the forward orreverse signals to be placed anywhere in the CATV band, either at highor low frequencies without signal to noise ratio concerns. Moreover, inthe forward direction, the carrier signals are minimized so that carrieroverloading does not occur and that the 3 MHz channels can be placedwhere space is found.

FIG. 3C illustrates an alternative frequency allocation for a split bandCATV network that is implemented in an alternative embodiment of thepresent invention, described in connection with later figures. As inprior embodiments, the frequencies used for television programming thatgenerate the revenues for the system operator are generated in theforward band from 50 MHz and above. The spectrum in FIG. 3C includes thereverse band from about 5 MHz to about 30 MHz. The 5-30 MHz band is usedfor upstream telephony signals in the form of 388 DS0's, combined toform DS0 pairs and QPSK modulated in 128 kHz upstream channels orsubbands designated UP1, UP2, . . . UP194, where each upstream channelUPn carries 2 DS0's. Thus, in order to accommodate 388 DS0's, 194 QPSKcarriers or channels are required. Each of the upstream channels UPnconsumes 128 kHz bandwidth, comprising 108 kHz of modulated signal spaceand 20 kHz of guard band. The modulated digital signals are as formattedas described in connection with FIG. 9B.

The downstream telephony is provided in downstream channels DN1, DN2 . .. DN480, each DN corresponding to a DS0. In the preferred alternativeembodiment, a total of 15.840 MHz of bandwidth is provided in 3.168 MHzsubbands, each 3.168 MHz subband carrying the equivalent of DS2telephony signal (96 DS0's), in QPR modulation, formatted as describedin connection with FIG. 9C.

A detailed block diagram of the input interface 32 is illustrated inFIG. 4. The function of the input interface 32 is to convert the 20 DS1telephony signals into the five QPR modulated RF signals which are sentto the subscribers in the forward band of the CATV system 12. The inputinterface 32 is connected to an optical interface 40, comprising a fiberoptic receiver 45 and a demultiplexer 44. The fiber optic receiver 45operates to convert the optical signal into an RF digital signal of astandard telephony format. The demultiplexer 44 receives the digital DS3telephony signal and separates it into its 28 component DS1 signals,where each DS1 signal comprises 24 DS0 signals. The optical interface 40also allows an addressing and control unit 42 to decode and stripoverhead and framing bits from the signal.

The input interface 32 comprises a series of five multiplexers 46, whicheach take four of the DS1 signals from the demultiplexer 44 and combinethem with signaling and addressing bits from the addressing and controlunit 42 to form a 6.312 Mb/sec serial digital signal. Each of the fivedigital signals is modulated on a selected carrier frequency by anassociated QPR modulator 48. The five telephony channels from theoutputs of the modulators 48 are frequency division multiplexed togetherin an RF combiner 50 before being inserted conventionally on the CATVnetwork 12.

The output interface 34 will now be more fully described with referenceto FIG. 5. The output interface 34 functions to convert the 480 DS0digital signals which are QPSK modulated on the reverse band carriersinto the optical format for coupling to the telephony network 10. Theoutput interface 34 extracts the reverse band signals in a conventionalmanner and fans them out with a signal divider 60 to a plurality oftuner/demodulators 62. Each of the tuner/demodulators 62 is adapted totune one of the carrier frequencies of the reverse band signals anddemodulate it into a DS0 format digital signal. The tuners of thetuner/demodulators 62 can be variable or fixed, or can be adapted totune only certain bands of the reverse spectrum. The output of thetuner/demodulators 62 is 480 DS0 signals which are concentrated intogroups of DS1 signals by a group of multiplexers 64 under the control ofaddressing and control unit 66.

Each of the multiplexers 64 inputs 24 DS0 formatted signals and outputsone DS1 formatted signal to a fiber optic transmitter 49. At the fiberoptic transmitter 49, the 20 DS1 signals are concentrated by amultiplexer 68 into a single DS3 digital signal which is input to theoptical transmitter 70. The addressing and control unit 66 adds thenecessary control information in the optical transmitter 70 beforecommunicating the digital DS1 signals in an optical format. The opticaltransmitter 70 also converts the RF signal into light so the opticalfiber of the telephony network can transmit it.

A detailed block diagram of the system equipment at the subscriberpremises 30 is shown in FIG. 6. Generally, the subscriber will want tomaintain CATV video or other services and has a CATV terminal 84 forthis purpose connected between the CATV drop line 28 and a televisionreceiver 88. The CATV terminal is connected to asplitter/combiner/diplexer 80 coupled to the drop 28 from one of theCATV coaxial subnetwork feeders.

Because the presently described broadband communications system does notinterfere with or displace the conventional CATV programming andfrequency allocations, the CATV terminal 84 can generally be used withno modification or change in operation of the installed terminal base.The system operator does not need to change or reconfigure itsdistribution network operation and the new telephone service iscompatible with its installed CATV subscriber terminal base.

The broadband communications service is provided by coupling a telephonyterminal, also called a "customer interface unit" 82, between thesplitter/combiner/diplexer 80 and the telephone equipment 86. Thecustomer interface unit 82 converts the incoming telephony signals to asubscriber into analog signals which can be used by a standard telephonehandset 86 over a pair of twisted wires 85. Further, the customerinterface unit 82 converts the analog signals, representing outgoingtelephony signals from the handset 86, into a QPSK modulation which iscoupled to the CATV network. A standard telephone handset 86 is shownfor the purpose of illustration but could in fact be any equipmentnormally connected to a telephone line for digital communicationspurposes.

The telephony terminal 82 has two communication paths. The first pathfor incoming signals comprising a tuner/demodulator 92, demultiplexer96, and a portion of line cards 98a-n and a second path for outgoingsignals including a portion of the line cards 98a-n and a plurality ofmodulators 94a-n. The tuner/demodulator 92, modulators 94, demultiplexer96, and line cards 98 are under the control of an addressing and controlunit (CPU) 90.

For incoming telephony signals which are received in the 3 MHz channelsmodulated on an FDM carrier, the control unit 90 causes thetuner/demodulator 92 to tune the carrier on which the particular callinformation directed to the subscriber is carried. The carrier definesone of the five 3 MHz channels having 4 DS1 or 3 E-1 telephony signalsQPR modulated thereon.

The telephony signals are demodulated by the tuner/demodulator 92 into aserial digital stream containing the 4 DS1 or 3 E-1 telephony signalsbefore being input to the demultiplexer 96. The demultiplexer 96 selectsthe particular DS0 digital telephony channel assigned to the subscriberat the input rate of 64 kb/s and inputs the data to an input terminal ofthe line card 98. The control unit 90 determines which forward telephonychannel to tune and which DS0 signal to select from that channel fromthe signal and addressing information it receives by its connection tothe splitter/combiner/diplexer 80 via line 89.

The DS0 digital format provides a voice channel with sufficientbandwidth for voice quality communications. The DS0 format is a 64 kb/sdata stream of bytes forming timed samples of an analog voice signal.This produces a voice signal quantized to 8-bits per sample (256 values)at a sampling rate of 8 kHz and with a bandwidth of 4 kHz.

The line card 98 receives the digital telephony signal in the DS0 formatand converts it to the proper analog voltages and signals to drive thetelephone handset 86. In addition, the line card 98 provides ringingcurrent, terminal identification, and other standard functions under thedirection of control unit 90. The line card 98 receives the analogtelephony signals from the telephone handset 86 and converts them into adigital DS0 format. Dialing signals and other addressing and controlsignals from the handset 86 are also digitized by the line card 98. Thedigitized outgoing telephone signals are then combined and formatted bythe line card 98 into a DS0 format at 64 kb/s and input to the modulator94.

The modulator 94 under the regulation of the control unit 90 selects acarrier frequency in the reverse band and QPSK modulates the DS0telephone signal thereon. The QPSK modulated carrier having a bandwidthof approximately 50 kHz is coupled on the CATV network through thesplitter/combiner/diplexer 80.

FIGS. 7A and 7B illustrate a detailed block diagram of the conversionmeans for converting 4 DS1 digital format signals into a DS2 digitalformat signal. Each of the DS1 signals, if delivered by a standardtelephony optical receiver such as the fiber optic receiver 45 shown inFIG. 4, will be at analog voltages and differentially for transmissionover a subscriber loop. This signal is transformed into digital signallevels by a transformer 51 which then serves as the input to a clockrecovery circuit 52 separating the DS1 signal into a data stream andclock pair. The data and clock pair at the DS1 data transmission rateare input to an 8-bit buffer 53. The buffers 53 are to allow for thetime base change from the DS1 data rate to the DS2 data rate in amultiplexer 54. The multiplexer 54 takes the data from each of the fourbuffers 53 and multiplexes them into a single channel of data outputthrough a buffer amplifier 55 to the QPR modulator 48. The clock for theDS2 format data is derived from an oscillator 56 which drives themultiplexer 54.

Each of the buffers 53 are enabled to transmit data to the multiplexer54 by indicating that they are almost full, which is termed a STUFF REQ.When this condition occurs, the buffers 53 are enabled to transmit thedata at the DS2 data rate until they are empty enough to allow the DS1signals to fill them again.

The multiplexer 54 comprises basically a 4:1 multiplexer which takes twoof the DS1 channels in a non-inverted state and the other two in aninverted state and time division multiplexes them into a serial datasignal which is then randomized by a PRBS randomizer. The randomizeddata is then framed by a data framer, and finally resynchronized to theDS2 data rate by the DS2 clock.

Control for the buffers 53 and the multiplexer 54 are provided by amultiplexer control comprising counters and decoders. The multiplexercontrol further controls two multiplexers which provide the data andframing bits for the DS2 signaling overhead at the correct times andcorrect places in the signal.

A more detailed schematic diagram of the modulator 94 for each terminalis illustrated in FIG. 8. The modulator functions to change the datarate from the 64 kb/s voice signal at the line card to 68 kb/s, therebyallowing framing bytes to be added to the signal. The modulator alsocombines the data with a pseudorandom bit sequence (PRBS), whichrandomizes the data for transmission over the CATV network. The signalis then QPSK modulated on a carrier using differential encoding.

Referring now to the FIG. 8, the voice data, after being digitallyencoded, is shifted into a three stage buffer 100 at 64 kb/s and shiftedout of the buffer 100 at 68 kb/s. This allows an extra byte to be addedto the data stream at 16 byte intervals to produce a subframe of 17bytes. The specialized byte or framing byte is used for signaling, framerecognition, error detection and correction, or the like.

When the data stream has been increased in frequency, the signal is thenframed in a framer 102 which inserts the special framing bytes every 16data bytes. The framing format is similar to the European E-1 formatwhere bytes are added to a data signal in even and odd frame times. Tworeasons for this is because the DS0 format is already byte oriented, andbunched framing sequences are easier to frame on the nonbunchedsequences.

Then, a randomizer 104 acts on the data to distribute the energy of thesignal over longer time periods. It is known that such randomization isbeneficial for the clock recovery circuits of the demodulators at thecentral or headend location. The randomization is accomplished bygenerating a pseudorandom bit string (a "PRBS"), and then adding it byteby byte to the data signal. The longer and more random the string, themore randomizing effect that such operation has on the data. The PRBScan be generated in many ways, but the simplest is with a shift registerwhich continually recirculates the sequence wherein the preferredimplementation a 127 bit pattern is used. The output, as is well known,can be derandomized by subtracting the same sequence in the same orderwhich it was added to the bit stream.

The illustrated framing sequence or data format for the preferredembodiment is shown in FIG. 9A. The framing sequence or data format foran alternative embodiment of the invention is shown in FIG. 9B and FIG.9C, which is discussed below in connection with the alternativeembodiment.

In FIG. 9A, the framing is organized as even and odd subframes of 17bytes and where there are different frame alignment sequence (FAS) bytesfor each. The subframes are grouped into a multiples of 8 in amultiframe or superframe to allow for higher level activities such asCRC computation. The framing sequence is x0011011 in the even subframes,and x1xxxxxx in the odd subframes. The don't care (x) bits may be usedfor special conditions but are not important for framing. The framingpatterns use both the primary and secondary FAS values to insure nofalse framing locations appear in the data. The primary FAS must have 7bits to match while the secondary FAS has only one bit, but it is in alocation where the primary has a zero. If the primary pattern isencountered in the data, then the chances of a data one beingencountered simultaneously in the secondary FAS are low.

The framer 102 can be operated in two modes, one with a cyclicredundancy code (CRC) and one without a CRC. If the first bit in each ofthe FAS bytes is always one, then a CRC is not used and there are onlytwo subframes (no multiframe). If the first bit in the odd subframes isthe pattern shown in FIG. 9, then the CRC multiframe is recognized. Thedefinition of the multiframe allows carrying of a CRC remainder in thefirst bit of the FAS in the even subframes. The bits C1, C2, C3 and C4will carry a CRC-4 remainder for the previous frame. The CRC computationis X⁴ +X+1 which is defined by the CCITT G.704 for use with the E1telephony format. The CRC computation will indicate the quality of thedata transmission. This framing format allows for alternate use of eachchannel as a data transmission channel. Any 64 kb/s data stream can betransmitted (data or voice), which will allow for support of directdigital services (DDS).

One of the primary advantages of the present invention is its frequencyagility, and the ability to allocate bandwidth to subscribers on demand.The frequency agile feature is preferably provided in the reverse bandof the communications system, and is operative for modulating atelephony signal from a subscriber in one or more frequency subbands inthe reverse band of the subscription network so as to provide selectablyvariable bandwidth in the second band commensurate with selectedsubscriber communication features. For example, a subscriber cansubscribe to a single voice grade line telephone service, plural voicegrade telephone line service, ISDN telephone service, local or wide areanetwork communication services (e.g. ETHERNET, Appletalk), securitymonitoring communication services, or the like.

The DL bits form a 500 bits per second data link. The data link will usean HDLC level formatter to send message packets or bit oriented statusinformation. The AL bit is an Alarm bit which indicates a problem at theline card. A data bit value of 1 signals no Alarm, and a data bit valueof 0 signals Alarm. The bits A, B, C and D are the signaling bits whichprovide for sixteen possible signaling states. It is evident that morestates can be defined by toggling the bits at certain rates. Thesignaling bit definitions are: bit A=1 on hook; bit A=0 off hook; bitB=1 not ringing; and bit B=0 ringing. The status of the appropriatestatus detector will be read once every 4 ms and inserted into theproper bit locations in the odd FAS.

The RF modulator 106 accepts a 68 kb/s data stream to QPSK modulate a RFcarrier (5 MHz to 30 MHz) and transmits the information via the coaxialcable subnetwork in a 50 kHz channel to the headend. The digital data issplit into I and Q channels by the encoder 108 and differentiallyencoded to remove phase ambiguity in the carrier recovery at thereceiving end. The I and Q channels of encoded information are thenfiltered separately in filters 110 to ensure that the data can betransmitted with a minimum of intersymbol interference. The filters 110are digitally implemented and approximate a raised cosine filter with analpha=1.5. Separate filtering at baseband allows for lowpass filters tobe used instead of a more complex bandpass at the output of themodulator.

The I and Q signals are then amplified to appropriate levels in order toassure proper operation of the mixers. The quadrature modulator 112generates two phase locked IF carriers, 90° out of phase, each of whichare PSK modulated with one channel of the encoded and filtered data.

The two channels are recombined to produce a quadrature signal andamplified prior to being frequency translated to the appropriatetransmit channel. The translation operation is frequency agile, and thetransmit channel is programmable through the forward data link. Thetransmit signal is then amplified by a buffer amplifier, thus permittinga fully loaded system with 480 channels to produce approximately thesame loading as would 5 video channels in the reverse band.

The demodulator 480 for the QPSK signal, which is 50 kHz in bandwidth,will be more fully described with reference to FIG. 10. The particularcarrier frequency in which the QPSK signal is modulated is tuned by aconverter 114 having as an input the channel number from the address andcontrol unit 90. The converter 114 selects the particular frequency andconverts it to an intermediate frequency, preferably 455 kHz. Theintermediate frequency signal is filtered by a band pass filter 116 andthen amplified by an amplifier 118 with automatic gain control. Theclock for the QPSK signal is recovered through an envelope detector 120and a band pass filter 122 which passes the symbol rate, in this case 32kHz to a comparator 124. This clock is used to clock two D-typebistables which sample the I and Q phases of the QPSK signal. Thesamples of the I and Q phases are differentially decoded and thenconverted from parallel to serial in converter 126 and thereafter outputas a 64 kb/s digital signal.

The demodulation takes place in a two path demodulator which multiplieseach phase of this signal by a recovered carrier from a VCO 128. The VCO128 is nominally at four times the symbol rate and is divided into anin-phase path and a quadrature phase path. One phase of the carriersignal is applied to a double balanced modulator 130 which produces abalanced output demodulated signal and its inverse, which are thenfiltered by a low pass filter 132 and differentially compared by acomparator 134 to become the input to the D-type bistable. The otherphase of the carrier is applied to a multiplier which demodulates theintermediate frequency signal by the recovered carrier and then low passfilters the result and applies it to a comparator. The output of thecomparator becomes the input to the D-type bistable where it can besampled at the symbol time to decode the value of the bit.

The carrier is recovered by driving the voltage control oscillator 128from the output of an integrator 136 which differentially compares thephases of each of the demodulated signals and their inverses throughmultiplexers. The multiplexer inputs are selectively controlled from thevalues of the signal channel and inverse outputs.

In summary, the present invention provides for broadband communicationsincluding digital communications, telephony, and telephony-relatedservices by utilizing a CATV system in an efficient manner, while notrequiring extensive switching equipment and a redesign of such systems.The broadband communications system requires no switching in the normalcontext when connecting telephony based calls from a subscriber or to asubscriber. A multiplicity of calls can be placed through the systemefficiently using the broad bandwidth of the CATV network to utilize itsbest features and having the switching for the connection of the callsperformed by the telephony network to utilize its best features.

There are two types of telephony calls in the broadband communicationssystem, where one is an incoming call and the other is a outgoing call.With combinations of these types of calls, all the necessary connectionsto or from another telephony set and to or from a CATV networksubscriber can be made. The subscriber may call (or be called by)another subscriber within the CATV network system, may call (or becalled by) a local telephone set within the local area of the telephonenetwork, or may call (or be called by) the telephone network tointerface to the long distance and international telephony systems.

An incoming call is directed to a particular subscriber of the CATVnetwork by the telephony network recognizing that the call is directedto one of the group of subscribers belonging to the CATV network. Thecall is then switched by the telephony network to the OC-1 or otherstandard telephony signal coupled to the CATV network in the time slotassigned to that subscriber. The addressing and control system of theCATV network then decodes the multiplexed information and translates itinto a frequency and time position in the forward multiplex that hasbeen assigned to the particular subscriber. The addressing and controlsystem further provides the necessary control for causing the subscriberequipment to ring or alert the subscriber of an incoming call.

The telephony network and CATV network maintain the connection untilthere is an indication of an "on hook" signal by one of the parties oranother signal that indicates that the communication is complete, suchas an end of message data pattern or the like. What is meant bymaintaining the connection is that the telephony network continues toplace the called party's data packets into the assigned DS0 position inthe standard telephony signal and the broadband communications systemcontinues to convert them to the location and frequency in the forwardmultiplex that is directed to the particular subscriber.

For outgoing calls, the telephony network recognizes from the DS0position in the standard telephony signal which data packet belongs to aparticular originating subscriber of the CATV network. This is anassigned position and the CATV system converts data on whatever carrierfrequency is input to the demodulators to that assigned position in thereverse multiplex. Therefore, for outgoing calls the telephony networkwill consider the standard telephony signal as a group of individual DS0signals, whose location in the reverse multiplex identifies theoriginating subscriber.

Alternative Embodiment--Selectable Bandwidth Allocation

Turning next to FIG. 11, the preferred embodiment of a headend interfaceunit (HIU) 301 constructed in accordance with an alternative embodimentof the present invention will be described. The alternative HIU 301 issuitable for use either as equipment comprising the headend 14 orequipment comprising the fiber node 16 shown in FIG. 1, both of whichare operative for receiving multiplexed digital telephony signals in astandard telephony format such as DS3, DS2, DS1, and coupling suchsignals to an input interface 32, 36 or an output interface 34, 38.Although the preferred embodiment is described in connection with acoaxial line HIU, it will be understood that the principles areapplicable for an optical-fiber based HIU that employs methods forcommunicating broadband signals via amplitude modulation (AM) methods,such as described in U.S. Pat. No. 5,262,883, which is owned by theassignee of the present invention. Briefly described, the HIU 301 isoperative for connecting to a telephone company (telco) standardmultiplexed telephony signal, directing incoming telephony signals tosubscribers downstream on the broadband network using QPR modulation inthe forward path, and receiving outgoing telephony signals fromsubscribers upstream on the broadband network in one or more selectedsubbands within the reverse path spectrum, commensurate with servicelevels or features elected by subscribers.

The alternative HIU 30 1 shown in FIG. 11 is a presently preferredembodiment involving the use of digital line cards 303 that providedigital signals to a digital bus or backplane 305, operating togetherwith a central processing unit (CPU) 308 corresponding to the addressand control unit 42 as shown in FIGS. 4 and 5.

The HIU 301 comprises a plurality of DS1 line cards 303a . . . 303n,where n is 17 in the disclosed embodiment, for connection to thetelephony network 10 or to a higher level multiplexer/demultiplexercapable of handling higher level multiplexing such as DS2 or DS3. Itwill be recalled that each DS1 corresponds to a T1 line, each T1 linecomprises 24 DS0 standard telephony channels. For provision of 388DS0's, therefore, slightly more than 16 DS1 's must be accommodated.With 17 DS1 line cards 303, a number of lines are provided as spares.

Each DS1 line card 303 provides interfaces compatible with ANSI Doc.T1.403 (1989 version), which is incorporated herein by reference andmade a part hereof. Each line card 303 provides a digital output signalthat is coupled to the digital backplane 305. The backplane operates toconnect all of the line cards 303 and route signals between the linecards and the forward and reverse path modulators, to be described. Thebackplane 305 preferably comprises up to five 8-bit serial digitalbusses each clocked at 8.192 MHz. Each bus thus provides an 8.192Megabit per second (Mb/s) digital pathway that is operative to receivedigital signals from each of the line cards in a time division multipleaccess (TDMA) format. It will be appreciated that five 8.192 Mb/sdigital busses in parallel are sufficient to handle the 388 separate 64kbps signals.

The backplane 305 further includes a CPU bus coupled between a CPU 308utilized as a database controller and each of the line cards 303 The CPU308 is operative to control the assigned relationships betweenparticular telephony lines, ingoing and outgoing, with predeterminedcarrier assignments in the reverse path and in the forward path, monitorthe noise level in the reverse path, and assign DS0 channels in thereverse path commensurate with subscriber features and the like.Further, the CPU 308 is operative to carry out steps described below ofmonitoring noise in the reverse pathway channels as described inconnection with FIG. 16, and dynamically allocate bandwidth as describedin connection with FIG. 17, and to maintain in memory a service leveltable as shown in FIG. 15 that indicates the correspondence betweenreverse channel carrier frequencies, subscriber identification, servicelevel, telco DS0 identification, signaling status, error count for noisemonitoring, and the like.

The preferred CPU 308 is a Motorola 68360 32-bit microprocessor withbuilt-in memory (DRAM) controller and is operatively connected to 2 MBof random access memory (RAM). Details of the preferred CPU areavailable in the literature supplied by the manufacturer.

Still referring to FIG. 11, the backplane 305 further includes asignaling channel bus connected between the CPU 308 and each of aplurality of forward channel modulators 320 and reverse channeldemodulators 330. The signaling channel bus communicates statusinformation associated with a telephony line such as off hook, on hook,busy, ring, security status, and the like. Bits associated withparticular status states of the subscriber's telephone and of theassociated telco line are included and combined with digitized telephonysignals and transmitted to the CIU's 400, as described below.

In the disclosed embodiment, the HIU 301 comprises a plurality offorward channel modulators 320a . . . 320n and a plurality of reversechannel demodulators 330a . . . 330m. The forward modulators 320 coupleoutgoing telephony signals to the broadband network in the forwardspectrum, while the reverse channel demodulators receive telephonysignals from CIU's in the reverse spectrum via the broadband network.Each of the forward channel modulators 320 is connected to a combiner322 that is operative to combine the RF signals from the forward channelmodulator and provide an output to a diplex filter 325. The diplexfilter 325 is preferably a bandpass filter that passes signals outwardwithin the 15.840 MHz frequency forward spectrum provided in thealternative embodiment whose spectral allocation is shown in FIG. 3C.The output of the bandpass filter, whose frequency is centered at anappropriate location along the spectrum allocated for forward ordownstream telephony signals, is then coupled to a multiway splitter 340that is coupled to the broadband communication network.

It will be appreciated that the broadband communication network (notshown) connected to the multiway splitter can either be a coaxial cablenetwork, or alternatively can be an additional fiber optic link that isamplitude modulated to carry the broadband signal in a manner known tothose skilled in the art.

Still referring to FIG. 11, the HIU 301 further comprises a plurality ofreverse channel demodulators 330a . . . 330m that are connected toreceive signals from the multiway splitter 340. The reverse channeldemodulators are similarly constructed, as described in connection withFIG. 14. A separate reverse channel demodulator is provided for eachpossible frequency allocated in the reverse spectrum for upstreamtelephony signals; in the disclosed embodiment, therefore, m=194.

The multiway splitter 340 preferably includes at least one lowpassfilter segment that isolates the signals in the 5-30 MHz rangedesignated in the alternative embodiment for reverse path telephonysignals.

FIG. 12 illustrates a frequency agile customer interface unit or CIU 400constructed in accordance with the alternative embodiment of the presentinvention. The CIU 400 is utilized in the same manner as described inconnection above with the telephony terminal 82, and includes the samebasic components as described in connection with FIG. 6. However, thereare certain differences, as will be described.

The CIU 400 is especially adapted for utilization with selectablebandwidth features or services that may be subscribed to by subscriber,e.g., single line telephony service, multiple line telephony service,ISDN service, data communications service, local or wide area network ofdata communications such as ETHERNET, or the like.

In order to implement the on-demand selectable services and toaccommodate the varying bandwidths for such services, the CIU 400includes one or more line cards 98', which are constructed basically thesame as the line card 98 shown in FIG. 6. The alternative line cards 98'are of varying types depending upon the nature of the service that is tobe connected. For example, the line card in 98'a is adapted for twoconventional voice grade telephony line 402a, 402b that comprise theconventional 2-wire twisted pair copper connections with tip (T) andring (R) known to those skilled in the art. On the other hand, the linecard 98'b is adapted for ISDN and includes a standard ISDN connector.Other types of lines cards 98'n may be provided for connection of othertypes of customer data service such as local area network datacommunications (e.g. ETHERNET), security monitoring systems, videoteleconferencing, etc.

Thus, it will be understood that the line cards 98' include connectorssuitable for the particular type of data service to be provided onbehalf of the customer. For example, a line card configured forconnection to a security alarm network will include a compatiblephysical connector for connection to the customer's alarm system networkand will include circuitry for converting data from the alarm systemnetwork into the 64 kbps digital data stream provided for upstreamcommunications.

The standard telephony line card 98'a includes a pair of subscriber lineinterface circuits (SLIC) 405 that are adapted to receive signals onvoice grade telephony lines 402 and couple them to a coder/decoder(CODEC) 407 for digitization. The voice grade telephone lines 402 may becoupled to a subscriber's home wiring network so that a number ofsubscriber telephones connected in parallel may access a given telephoneline.

The preferred SLIC's 405 are type AM7943 or AM7949, manufactured byAdvanced Micro Devices in Sunnyvale, Calif. The CODECs 407 are operativeto digitize the voice grade telephone lines into serial 64 kbps digitaldata. The preferred CODEC's 407 are preferably type AM79C02,manufactured by Advanced Micro Devices.

The output of the codec 407 comprises a digital serial data that isoutput in response to commands from a control CPU 410 that serves in acapacity corresponding to the address and control unit 90 in theembodiment shown in FIG. 6.

An ISDN-capable line card such as 98'b is substantially the same as theline card 98'a, except that the SLIC circuitry is operative to providean appropriate ISDN connections, but still provides two 64 kbps digitaldata streams as outputs. The principal requirement of the line cards 98'are to provide a suitable physical connection for customer data in theform of standard output ports or connectors, and provide digital datastreams as outputs in response to commands from the CPU 410. Further,plural line cards may be provided at any given customer premises,depending upon the particular types of services to be provided to thecustomer.

It will be understood that the nature of the service that is provided atany given CIU 400 must be preidentified and prestored in memory in theHIU 301 that is utilized as the telephony network interface, so as toenable provision of the selected service upon demand. In response to arequest for service either originating with a subscriber at a selectedCIU, or a request for incoming service to a subscriber originating.externally to the network, status signals such as the subscriber goingoff hook, or a ringing condition on an incoming line, the system causesthe selection and allocation of appropriate bandwidth, DS0 channels,reverse channels, carriers, etc., required to provide the selectablyvariable bandwidth commensurate with the selected service.

Still referring to FIG. 12, the line cards 98', whether one or many, arepreferably connected to a backplane 412 in the CIU so that signals fromthe various line cards may be coupled to appropriate modulators anddemodulators and receive control signals from the CPU 410. The preferredbackplane 412 includes a 4.096 Mbps serial digital bus that is operativeto transmit 64 kbps data in a TDMA manner from a selected CODEC 407 in aselected line card to a selected reverse channel modulator 415. There isalso provided a second 4.096 Mbps digital bus for transmitting data froma forward channel demodulator 420 to selected CODEC 407 in a selectedline card for outgoing transmissions. The CPU 410 is operative tocontrol the selection of line cards, reverse channel modulators, andforward channel demodulators. While the preferred embodiment illustratesthe use of two 4.096 Mbps digital busses in parallel, it will beunderstood and appreciated to those skilled in the art that a single8.192 Mbps digital bus could also be used.

The backplane 412 in the CIU 400 further includes a signaling bus thatcouples control signals between the line cards 98' and the CPU 410. Thesignaling bus carries status signal associated with status of thetelephony lines such as off hook, on hook, alarm, busy, ring, forinclusion as a part of the status information associate with theselected service.

Outgoing data from the line cards 98' are provided to reverse channelmodulators 415 for provision to the broadband network. Each line cardgenerally provides a pair of DS0 (64 kbps) data streams, which arecombined and transmitted in the reverse path on a carrier by a singlereverse channel modulator 415. Details of the preferred reverse channelmodulator 415 are described in connection with in FIG. 13.

Incoming data from the broadband network is derived from at least oneforward channel demodulator 420, which is operative to monitor apreassigned channel in the QPR-modulated forward channel utilized forincoming telephony signals. The preferred forward demodulator 420operates in the manner described above to demodulate a QPR modulatedforward channel signal in the designated telephony downstream subband of15.840 MHz, and to monitor the directory channel and signaling channelsprovided as a part of the overhead data.

It will be noted that a plurality of reverse channel modulators 415a . .. 415n may be required to provide the appropriate bandwidth required fora given level of service. For example, if a selected service entails theequivalent of four DS0's, then there is the need for four reversechannel modulators 415. Furthermore, it will be recalled that eachmodulator 415 is frequency agile and is not necessarily operating at agiven fixed upstream carrier frequency, since upstream channels can bereassigned dynamically and in response to changing conditions such asnoise level and reallocation of bandwidth in response to thesubscriber's needs.

The plurality of reverse channel modulators 415 are connected to acombiner 425 so that the RF output signal can be coupled to the coaxialcable. The output of the combiner 425 is connected to a diplex filter430 that passes a signal in the 5-30 MHz range for coupling to asplitter 432 that is connected to the subscriber's coaxial cable drop.The diplex filter 430 is further operative to pass signals in theselected forward 15.840 MHz spectrum for downstream signals to theforward channel modulator 420 so that the directory channel, signalingchannel, and downstream telephony DS0's may be demodulated and coupledto the appropriate line cards.

The splitter 432 is conventional and operates to receive signals fromthe diplex filter 430 in the 5-30 MHz reverse channel and couple them tothe coaxial cable drop, to receive incoming downstream telephony signalsin the forward frequency band and couple them to the forward channeldemodulator 420, and pass signals above 30 MHz (in the conventional CATVprogramming spectrum) to the subscriber's television equipment.

It will be understood that the CIU 400 can be physically configuredeither as separate customer premises equipment located in or near asubscriber's telephony punch blocks, or as a CATV set top terminalincluding one or more RJ-11 or similar telephone connectors. Moreover,the CIU, since it includes a computer (CPU 410) and associated circuitrycan be used for conventional CATV signal management such as pay-per-viewcontrol, descrambling, etc. Therefore, the preferred CIU, whether settopor separate circuitry enclosure, includes a control connection providedfrom the CPU 410 to a switch 435 associated with the signal line betweenthe splitter 432 and the subscriber's television. This allows theprogramming signals to be disconnected from a subscriber in the event ofnon-payment or election not to receive a certain programming.

Finally, each CIU 400 is associated with a predetermined address in thenetwork. This address is preferably maintained internally, in aread-only memory. The address of the CIU is a 64 bit digital number thatis provided in the upstream channel to the HIU whenever the CIU requestsservice. The address information is utilized by the HIU to examine itsservice level table (FIG. 15) to identify the subscriber associated withthe address information and determine the appropriate and authorizedlevel of service to be provided. For example, when a telephone connectedto the CIU goes off hook, the address of the CIU is transmitted inassociation with the off hook status information in the upstream channelto the HIU, where it is received and examined to determine theappropriate service level, DS0 assignments, frequency assignment, etc.

FIG. 13 illustrates a frequency agile reverse channel modulator 415constructed in accordance with the alternative embodiment of the presentinvention. The reverse channel modulator 415 is operative to receiveserial data input from the digital bus in a CIU in the form of two DS0'sat 64 kbps, respond to controls signal from the CPU 410 (address andcontrol unit), and modulate the incoming data into a selected channel inQPSK for coupling to the reverse channel frequency spectrum. Themodulator is operative to provide the QPSK in a selected 108 kHzsubband, at a selected carrier frequency.

The preferred reverse channel modulator is constructed around a XILINXdigital controller 470, model no. XC4005, manufactured by Xilinx, of SanJose, Calif. The serial data controller 470 provides varying outputsignals to the other components as will be described.

The controller 470 receives the two 64 kbps signals from a connectedline card 98' and separates the data into two signal paths, I and Q, forthe quadrature phase shift keying modulation. The controller 470 alsoreceives 16 kilobits of overhead, which includes the framing alignmentsequence (FAS), the CRC remainder, and the data link that carries thesignaling information. The output comprises an output signal I DATA INat 72 kbps and Q DATA IN at 72 kbps. These are provided to a digitalNyquist filter 473 to obtain outputs designated FILTERED I DATA andFILTERED Q DATA. The controller 470 provides a gain control to theNyquist filter varying between 0 and -25 dB to the filter 473.

The Nyquist filter 473 shapes the modulated spectrum so that it will fitin the 108 kHz occupied bandwidth with zero intersymbol interference. Asa byproduct of the filter, gain control of 25 dB is obtained.

The FILTERED I DATA and FILTERED Q DATA outputs are provided to a pairof mixers 476a, 476b where the I and Q digital signals are beat with10.24 MHz 90° phase-offset intermediate frequency (IF) subcarriers. Thisyields a pair of quadrature-related QPSK signals.

The 10.24 MHz IF carriers fed to the mixers 476 are derived from an81.92 MHz phase locked loop (PLL) circuit 480 that is provided through adivide-by-eight (÷8) circuit 479 to obtain the 10.24 MHz IF subcarrier.The IF subcarrier is provided to the mixer 476a and through a 90° phaseshift circuit 482 to the mixer 476b. The outputs of the mixers 476a,476b are combined at a summing circuit 487.

The 81.92 MHz signal is also provided to a third mixer 485 which mixeswith the signal from the summing circuit 487. The output of the thirdmixer 485 is provided to a band pass filter 492 having a passband ofapproximately 3 MHz centered at 71.68 MHz so as to attenuate unwantedmixing products from the first three mixers. The 71.68 MHz output signalis downconverted by a down converter 490 which beats the 71.68 MHz QPSKsignal from the filter 492 with a 75-105 MHz RF carrier from a tunablephase locked loop (PLL) circuit 494 that serves as a frequencysynthesizer. The output of the down converter 490 is then low passfiltered by a low pass filter 496 to limit the output signal to below 35MHz. The RF output signal from the LPF 496 is a QPSK signal at aselected output frequency varying between 5.120 MHz and 29.824 MHz forthe reverse channel, selected as a function of the frequency provided bythe carrier emanating from the PLL 494.

The tunable PLL 494 receives its signal indicating the selected carrierfrequency for the selected upstream channel UP1, UP2, etc. via aCONTROL/FREQ REF signal from the controller 470. As it has beendescribed, the controller 470 receives the designated frequency foroperation of the reverse modulator from a control signal received bymonitoring the directory channel.

It will be understood that the described reverse modulator 415 shown inFIG. 13 may change its frequency very rapidly in response to commandsfrom the HIU when it is determined that a particular carrier in thereverse channel is experiencing excessive noise.

FIG. 14 illustrates a frequency agile reverse channel demodulatorconverter 114' utilized in the HIU shown in FIG. 11. It will beunderstood that one of the reverse channel demodulator converters 114'is provided for each pair of DS0 signals provided in one of the upstreamchannels UP1, UP2 . . . UP194 as shown in FIG. 3C. The reverse channeldemodulator converters 114', like their reverse channel modulatorcounterparts in the CIU, are frequency agile and can be selectivelytuned to predetermined carrier frequencies in the telephony upstreambandwidth of 5-30 MHz range. The embodiment shown in FIG. 14 ispreferably operative between 5.12 MHz and 49.9 MHz so as to allow forfuture expansion or utilization of the reverse channel bandwidth up toabout 50 MHz, which would allow additional reverse channel capacitybeyond the 388 DS0's of the described embodiment.

Each reverse channel demodulator converter 114' receives an RF inputsignal and provides it to an upconverter or mixer 520 where the incomingsignal is beat with a selectively variable frequency between 80 and124.8 MHz, that varies in increments of 128 kHz. The 80-124.8 MHz beatsignal is derived from a phase lock loop circuit 522 which is preferablya type MC 145170 manufactured by Motorola. The PLL 522 varies its outputfrequency as a function of a CONTROL signal provided from the headendunit (HIU) 301. The PLL locks to a 128 kHz signal fed from adivide-by-32 (÷32) circuit 525, which is driven by a 4.096 MHz clock.The CONTROL signal from the HIU that is indicative of the frequency towhich the circuit is tuned is provided on the signaling channel providedfrom the CPU 308 (FIG. 11). This signal varies from N=625 to 975,corresponding to output frequencies of 80.0 to 124.8 MHz.

The 128 kHz signal from the divide-by-32 525 is also provided to asecond divide-by-32 circuit 526 that derives a 4 kHz signal provided toa second phase lock loop circuit 528. The output of the second PLL 528is a 220 kHz signal that is then provided to a third PLL 530, whichprovides a stable 85.58 MHz output signal used for downconversion.

The reference frequency 4 kHz is first multiplied up to 220 kHz by PLL528 in order to more easily attenuate unwanted spectral byproducts fromthe output of PLL 530. Unwanted reference frequency sidebands aretherefore more easily filtered out since the reference frequency 220 kHzis more widely separated from the PLL 530's loop bandwidth(approximately 120 Hz) than it would be if the 4 kHz reference was useddirectly.

Referring back to the mixer 520, its output, which varies between 80 MHzand 124.8 MHz, is filtered through a bandpass filter 532 having apassband of approximately 3 MHz and centered at 74.88 MHz. The output ofthe bandpass filter 532 is provided to a mixer or downconverter 535. Thedownconverter beats the filtered input signal with the 85.58 MHz fromthe PLL 530. The output of the downconverter 535 is a 10.7 MHz signalthat is band pass filtered by an output band pass filter 538, whoseoutput is a 10.7 MHz carrier QPSK modulated signal that has beenretrieved from a selected 128 kHz subband within the 5-30 MHz reversefrequency range.

The output signal from the reverse demodulator converter 114' is thenprovided to a conventional QPSK demodulator that operates in the knownmanner to obtain the digital output signal comprising a pair of DS0's at64 kbps, as has been described.

It will be noted that the frequencies selected by the PLL 522 between80-124.8 MHz is chosen such that the output signal at 74.88 MHz is theselected signal containing the desired telephony signal in theparticular selected reverse channel subband 128 kHz wide.

Turn next to FIG. 15 for a discussion of the manner in which varyinglevels of the service are provided to a subscriber commensurate with aselected level of service and allocation of appropriate commensuratebandwidth to effect the service. The information illustrated in FIG. 15is stored in the CPU 308 in the headend interface unit (HIU) 301illustrated in FIG. 11. The CPU 308 stores in its memory a data tablethat correlates various information, e.g. the frequency of the upstreamchannel assigned to particular subscriber at a given instant in time,subscriber identification information, service level information, telcoline DS0 identifying information (i.e. the identity of the lines in themultiplexed input telephony signal provided from the telephone operatingcompany), signaling status information, error count and thresholdinformation indicative of noise level on a selected channel, and a"noisy channel" flag indicative of whether the noise in a selectedchannel has exceeded a predetermined threshold and therefore requires achange.

The table of FIG. 15 will be described in connection with examples ofvarying levels of service that may be elected by a subscriber. It willbe recalled that each upstream (128 kHz) channel carries two DS0 signalsat 64 kbps each, QPSK modulated. Thus, the first upstream channel UP1has a nominal carrier center frequency of 5.12 MHz, assuming that thesubband for the channel begins exactly at 5.064 MHz and extends to 5.192MHz. In the first example of a channel UP1, a subscriber identified asS1 has elected a default level of service, indicating one line of voicegrade telephony service at 64 kbps. The table indicates that thetelephone company (telco) DS0 line is DS0-6, which indicates that lineDS0-6 in the input multiplex is the appropriate input/output linecarrying communications for this subscriber at this particular instantin time. It will be appreciated that the telco DS0 number can beassociated with any particular channel, because of the frequency agilityof the reverse channel circuitry described herein.

The status of the line DS0-6 is indicated in FIG. 15 as being "on hook",and therefore inactive. There is also provided an error count andthreshold field associated with a channel, which in the example beingdescribed is not applicable (N/A) is the channel is inactive. The errorthreshold is indicated at 256, although this value is selectablyvariable according to the system operator. Finally, there is provided a"noisy channel" flag, wherein 0 equals OK or acceptable and 1 equalsnoisy. A "1" set in the noisy channel flag indicates a frequency changefor the reverse channel is to be effected, as the noise level has beendetected as excessive.

It will be recalled that each channel UPn carries up to two DS0 signals.Accordingly, FIG. 15 shows that the second DS0 capability for thechannel UP1 is unused for this example.

As a second example, note the functions associated with the subscriberidentified as S2. The subscriber S2 is shown allocated to the firstchannel frequency 5.248 MHz in UP2, and has elected two voice gradelines, which have been assigned to the telco DS0's DS0-7 and DS0-204.The signaling status field indicates that DS0-7 is "off-hook" andtherefore active. Conversely DS0-204 is indicated as on-hook andtherefore inactive. For the active line DS0-7, note that an error countof 6 has been stored in the error count field, which is within theacceptable threshold of 256.

Next consider the service level allocated to subscriber S3. Assume forthis example that subscriber S3 has elected basic rate ISDN telephonyservice, which comprises in the conventional configuration two bearer or"B" channels plus one data channel or "D" channel (2B+D). Each "B"channel is at 64 kbps and each "D" channel is 16 kbps, yielding 144 kbpsnominally. Those skilled in the art will understand that the primarysignal carrying function of ISDN service can be effected with only thetwo 64 kbps B channels; the D channel is optional for ISDN basic rateequipment and can be carried separately from the B channels. An ISDN2B+D "S" interface is called a basic rate interface (BRI), and normallyutilizes four unshielded normal telephone wires or two twisted pairwires to deliver two B 64 kbps channels and one D channel of 16 kbps.Each of the two 64 kbps B channels can be used to carry a voiceconversation, or one high speed data or several data channels which aremultiplexed into one 64 kbps high speed data line. The D channel of 16kbps carries control and signal information to set up and break downvoice and data calls.

For the subscriber S3 in FIG. 15, nominal ISDN service requires bothDS0's of the channel UP3, which have been assigned to the telco DS0channels at DS0-12 and DS0-13. To accommodate the D channel of ISDN, aquarter portion (1/4) of an additional DS0 channel is required if the Dchannel is to be transmitted together with the associated B channels.This is shown as assigned to a portion of the upstream channel UP4,assigned to telco DS0-144. All of these channels are shown as active andtherefore are accumulating an error count, all of which are below thethreshold of 256 and are therefore acceptable.

Next in FIG. 15, consider the service level allocated to subscriberidentified as S4. It is assumed in this example that a single subscriberS4 has elected T1 telephony service, which comprises 24 DS0's. These 24DS0's have been associated with telco channels DS0-155 through DS0-179.It will also be appreciated that to accommodate this many DS0 channelsat a CIU equipment, there must be provided a corresponding number ofreverse channel modulators, line cards, etc. T1 service is typicallyassociated with commercial use, whereas typical home equipment will onlyprovide for a few DS0 capability.

Next consider the service indicated by the subscriber identified as S5.A particular function that has been previously described is that ofsecurity monitoring services, as in the connection of a security alarmnetwork associated with a subscriber's premises to one of the line cards98' (FIG. 12). Accordingly, the upstream channel UP30 is assigned to thesubscriber S5, who has elected a security monitor service level. Thesignaling status indicates a "normal" status. Therefore, there is noneed to allocate a telco DS0 at this particular instant in time, in thatthere is no need to communicate any particular signals until an alarmcondition occurs.

In this regard, consider the subscriber S6, who has also electedsecurity monitoring service level. The signaling status indicates analarm condition, and a telco line identified as DS0-191 has beenassigned to this particular channel for monitoring of any signals thatmay be provided from the customer's security alarm network. The securitymonitoring signals are provided upstream to the HIU and thence via theDS0-191 line to a security service (e.g. for dispatch of an armed guardor for remote monitoring of the situation via data communicated throughthe system). Accordingly, it will be appreciated the bandwidthassociated with security monitoring is not necessarily allocated untilan alarm condition occurs, and that the bandwidth for upstreamcommunications need only be utilized in response to an alarm condition.

An alarm condition may be indicated in response to interruption of thecoaxial cable to a particular subscriber's equipment. It will berecalled from the discussion above that each CIU 400 containspredetermined address information that is transmitted to the HIU on theupstream signaling channel whenever service is requested by asubscriber, or when a channel is active. Likewise, the addressinformation is transmitted downstream in the directory channel so that aCIU can tune to the upstream channel commanded by the HIU or provide aring signal to a telephone connected to the CIU. The CPU 410 (FIG. 12)in the CIU is operative to monitor the forward directory channel forincoming signals addressed to it, and to provide an upstreamcommunication identifying itself and any relevant signaling informationon the assigned upstream channel UPn. Preferably, the addressinformation and signaling information from all CIU's are transmittedupstream to the HIU in response to a command from the HIU to tune to aparticular upstream channel frequency and transmit signaling informationincluding address and status. This is in effect a "polling" operationwherein a particular address CIU is responsive to a command or poll fromthe HIU to respond with a communication in a particular upstreamchannel. However, if the broadband communication line has been cut or amalfunction occurs, the CIU will not be able to transmit its address andstatus information to the HIU.

Therefore, in the event that the coaxial cable is cut and the CIU 400fails to communicate its identity and status information in response toa poll by the HIU, an alarm condition will be indicated and theappropriate status information will be indicated in the signaling statusfield in FIG. 15. In the preferred embodiment, the alarm conditioncauses the setting of an alarm status indicator in the service levelmemory associated with the particular subscriber so that remedial actioncan be indicated. It is expressly contemplated that the HIU can generateappropriate telephony messages to a security monitoring service so as toalert a security guard service as to the alarm condition.

Before leaving FIG. 15, it will be noted that the service level tablecomprises an array of data fields, suitable for storage in a databasemaintained by the HIU's CPU 308. Preferably, this table is maintained inRAM for rapid access. Furthermore, it is preferred that the table beindexed utilizing conventional database indexing methods so that thetable may be rapidly search by subscriber name, subscriber address,telco DS0 number, upstream carrier frequency, etc. Use of indexedmethodologies ensures rapid lookup of service level and minimizedresponse time when a subscriber requests service.

From the foregoing, it will be understood and appreciated that thefrequency agile CIU is operative for modulating telephony and othersignals from a subscriber in a plurality of frequency subbands in theupstream band of a broadband subscription network so as to provideselectably variable bandwidth in the upstream band commensurate with aselected subscriber communication feature such as single voice line,multiple voice lines, ISDN, security monitoring services, and the like.In the preferred embodiment, the bandwidth is selectably allocated indiscrete unit of DS0's, which will be understood can be combined toprovide for higher capacity digital data channels in response to varyingneeds of subscribers.

Furthermore, it will be understood that the frequency agile CIU isoperative to reassign signals in a selected subband, such as UP1 . . .UPn, to another subband at another frequency in response to adetermination that the noise level in a particular selected subbandexceeds a predetermined level.

Finally, there is provided at least one upstream signaling channel thatis utilized by each connected CIU 400 to provide signaling informationsuch as off hook, alarm conditions, together with address information.Each CIU 400 is normally assigned at least one upstream frequency(either the DS0-1 or the DS0-2 of the 128 kHz channel), which comprisesa portion of the 16 kbps data channels that is combined with two 64 kbpsdata channels to form 144 kbps for each upstream frequency subband. The16 kbps signaling and status information includes the subscriber'saddress as well as status information associated with a subscriber'saddress.

In this regard, turn next to FIG. 16 for a discussion of the manner inwhich the present invention operates to monitor noise level and allocatefrequencies.

FIG. 16 is a flow chart illustrating a sequence of operations wherein acalling subscriber initiates a communication and a request fortelephony, and the equipment responds by allocating bandwidth anddesignating an upstream channel, broadcasting the identity of a selectedchannel in a downstream directory channel for receipt by the requestingCIU, measurement of signal quality in the channel, etc.

The process begins in step 601, where a calling subscriber initiates atelephone call by going "off hook" with telephony equipment connected toa line card 98'. Generally, the first step taken is to provide a signalindicative of the changed status of the telephony equipment in theupstream direction to the HIU equipment.

The change in status from "on hook" to "off hook" is communicated in theupstream signaling channel designated for use by the associated CIU. Asdescribed in connection with FIG. 17, the changed status data iscommunicated upstream to the HIU 301 together with the CIU's address;the HIU is responsive to determine if it is appropriate that thisparticular subscriber remain at the designated upstream channel forcommunications of the telephony signals. In embodiments that utilize asingle signal frequency for signaling channel purposes that is accessedby all CIU's in a TDMA fashion, a channel will be assigned for the voicechannel communications and this information will be transmitteddownstream in the forward channel.

Assuming that a reverse channel has been assigned, the next step takenat 604 is to begin an analog to digital (A/D) conversion of thetelephony signal in the line card 98' associated with the requestingsubscriber, utilizing the CODEC 407 to obtain a digital data stream. Thedigital data stream is combined at steps 608 with framing bits by theCIU's CPU to obtain the frames and superframes as described inconnection with FIG. 9C.

At step 612, a CRC computation associated with the subframes andsuperframes is computed and added in the appropriate fields within theframe and subframe. At step 615, the superframe is provided to the QPSKmodulator, where it is transmitted on the broadband network upstream onthe designated subband for upstream communications.

At the HIU 301, which corresponds to the addressing and control unit 90in other embodiments, the particular upstream carrier frequency that wasassigned for upstream communication is also provided to a selectedreverse channel demodulator converter 114' as has been described inconnection with FIG. 14. The converter 114' at step 620 then tunes tothe designated upstream channel UPn. At step 625, the QPSK demodulatorthen demodulates the signal into the 144 kbps data stream. The datastream is formed into the superframe by examining the framing bits fordelimiting the superframe.

In step 630, the CRC values associated with the superframe are examined,and if the CRC is incorrect, the error count shown in FIG. 15 associatedwith a designated upstream channel is incremented. In the event that theerror count exceeds the predetermined threshold within a predeterminedtime period, as measured by the HIU computer, it is deemed that thechannel is excessively noisy. This is shown at step 632. At step 635,the error count is compared on a periodic basis to the predeterminederror count threshold to determine if the noise exceeds acceptablelevels. At step 635, so long as the signal quality is acceptable, thereis no need to change frequencies for upstream communications. On theother hand, in response to a determination that the error count exceedsthe predetermined threshold from step 635, the HIU 301 is operative tochange the carrier frequency.

If the signal quality at step 635 is acceptable, the method returns tostep 605 and continues to transmit telephony data in the mannerdescribed.

In the event of a detection of an error, the data is not retransmittedfrom the CIU to the HIU. Rather, the data is demodulated and provided atstep 640 to the telco line associated with a particular subscriber forcommunications on the telephony network.

FIG. 17 illustrates the preferred method of dynamic bandwidth allocationin response to selected levels of service requested by subscribers.There are two pathways for invoking the method involved with dynamicbandwidth allocation on behalf of a customer: (1) when a callingsubscriber initiates a request for telephony service originating at CIU,and (2) when an incoming call is received for a subscriber on aparticular incoming telco DS0 line from the telephony network. Bothpathways require that the system determine the appropriate level ofservice, and commensurate bandwidth, for the call. These steps are shownat 701 and 702, respectively. It will be appreciated that the remainingsteps are substantially the same regardless of whether the subscriberinitiates a call or an incoming call is received for the subscriber.

In a case where the calling subscriber initiates the call at step 701,the procedures described in connection with FIG. 17 of providing the"off hook" status information is provided in the designated upstreamchannel to the HIU 301, so that an appropriate upstream channel can beassigned, if one is not assigned by default.

Next referring to step 705, in response to receipt of the statusinformation indicating a request for service (such as an "off hook"status), or receipt of an incoming call at the HIU, the identity of thecustomer is ascertained by inspecting the service level table maintainedin memory by the HIU 301.

At step 708, the requested and authorized service level for theidentified customer is ascertained. This entails determining, forexample, that the subscriber has requested service such as ISDN and isauthorized to receive ISDN service, or other similar service levels suchas single line voice, multiple line voice, data communications, securityservices, etc.

At step 711, after the appropriate authorized and requested servicelevel has been ascertained for the particular subscriber, the number ofDS0's required for the selected service level are determined. Forexample, ISDN requires at least two DS0's (and possibly more if 2B+Dservice is provided), a single regular voice channel requires one DS0,plural voice channels require plural DS0's, security requires periodicmonitoring of the CIU, etc.

At step 713, the selected number of required DS0 data channels isdetermined, by using an index to the service table that is sortednumerically by telco DS0 number, to determine which DS0's are unused andmay be selected and assigned for use to satisfy the service request.Likewise, a corresponding number of reverse channels UPn are determinedfor the selected service level. It will be recalled that in thedisclosed embodiment, there are 388 available DS0 data channels in thereverse spectrum.

At step 715, the selected one or more DS0's in the reverse channel areassociated with particular DS0 channels from the telephony network, orin the case of an incoming call, the particular incoming DS0 line fromthe telephony network is associated with the selected one or more DS0'sin the reverse channel. The selected DS0's are then assigned to one ormore corresponding reverse channel frequencies UPn. In this regard, theservice level table of FIG. 15 is updated to reflect the correspondencebetween telephone DS0 channel numbers and reverse channel frequencies inthe upstream spectrum. This is carried out by inspecting the servicelevel table to determine available reverse channels.

Finally, at step 720, selected reverse channel frequencies aretransmitted to the particular subscriber in the forward directorychannel, by transmitting the CIU address and upstream channelidentification. The identity of the forward channel DS0 is alsoidentified in the service level table for incoming signals in theforward directory channel so that incoming signals from the telephonynetwork can be routed to an appropriate forward channel frequency andDS0 channel for provision to the subscriber CIU, which monitors theappropriate DS0 channel in the forward spectrum. In this manner, it willbe understood and appreciated that bandwidth may be allocated in aselectably variable manner so as to provide for appropriate levels ofservice that have been selected by a customer.

Referring now to FIGS. 9B and 9C, the data framing or data format forthe reverse path and forward path digital data as utilized in analternative embodiment of the invention will be described. In FIG. 9B,the reverse path data format, which is transmitted upstream in QPSKmodulation, comprises four subframes of 27 bytes to form a singlesuperframe. Each subframe is identical and includes a framing byte (FB)of eight bits, two data link (DL) bytes each containing eight signalingbits, and twenty-four DS0 data bytes (192 bits). The DS0 data bytesportion is formed by the multiplexing of the two DS0s.

A superframe is comprised of four subframes, and a CRC is computed overthe superframe block. The framing byte of each subframe comprises sevenbits of synchronization and one bit CRC. There are thus four bits of CRCtransmitted with each superframe, which comprises the CRC remainderassociated with the immediately preceding superframe.

The DL bytes of each subframe are used to carry messages that indicaterequired telephony signaling such as on hook and off hook in theupstream direction. In the preferred alternative embodiment, theassociation between a subscriber's CIU and the signaling is effected bythe HIU addressing and control unit 42 (FIG. 4) or HIU 301 (FIG. 11).The association between a subscriber's CIU and an on hook or off hooksignal is preferably determined by the predetermined association of aparticular reverse channel frequency with a particular CIU address,which is maintained in the service level table maintained by the HIU.Alternatively, the association could be made by providing addressinformation in the DL bytes that indicate which particular subscriber'sequipment is indicating the particular signaling.

For noise monitoring purposes, each subframe includes a CRC bit as apart of the framing byte (FB), and each of the subframes also include aCRC bit indicative of the CRC calculation for the entire superframe. Asdescribed elsewhere in connection with the alternative embodimentherein, an incorrect CRC calculation on a received superframe isindicative of noise in the channel and an excessive number of such CRCerrors exceeding a predetermined threshold causes the carrier frequencyto be changed in accordance with the alternative embodiment.

FIG. 9C illustrates the data format or framing in the forward path,which is transmitted downstream in QPR modulation. As in the preferredembodiment, the framing is organized as even and odd subframes of 99bytes. The subframes are grouped into multiples of eight in a multiframeor superframe to allow for CRC computation. In contrast to FIG. 9A, thedata format for the forward path in the alternative embodiment includesa 1 byte allocation for a directory channel (DIR), 1 byte for asignaling channel (SIG), and 96 bytes allocated to the telephony data,comprising 96 DS0's for each carrier. It will be observed that thedirectory channel (DIR) and signaling channel (SIG) are included in eachsubframe in the forward path. The DIR and SIG channels are thereforecontinuously broadcast to all forward path demodulators associated withthe CIU's so that each CIU can continuously monitor the directorychannel and respond rapidly to a command to change frequencies in thereverse spectrum, if necessary, and to respond very quickly to signalingthe information provided to a particular CIU, e.g., a ringing conditionfor a selected subscriber telephone. In order to accommodate thedirectory channel (DIR), there is provided up to 480 address wordsfollowed by indicia indicative of a selected channel that a particularaddressed CIU is to utilize for its reverse channel communications,together with appropriate signaling status information associated withthe addressed information.

While there has been shown and described the preferred embodiments ofthe invention, it will be evident to those skilled in the art thatvarious modifications and changes may be made thereto without departingfrom the spirit and scope of the invention as set forth in the appendedclaims and equivalents thereof.

What is claimed is:
 1. A bidirectional signal communications system forreceiving a multiplexed input signal comprising a plurality of inputdata channels and for providing a multiplexed output signal comprising aplurality of output data channels, wherein each input data channel inthe multiplexed input data signal corresponds to a particular one of aplurality of destinations connected via a broadband communicationsmedium and wherein each output data channel corresponds to a particularone of a plurality of origins connected via said broadbandcommunications medium, said system comprising:a first converter forconverting data in said input data channels into modulated downstreamcarriers in downstream channels associated with particular destinations;a first transmitter for transmitting said modulated downstream carriersto said plurality of said destinations; at least one demodulator fordemodulating an assigned carrier of said modulated downstream carriersat a destination and recovering incoming data in a particular datachannel associated with said particular one of said destinations; atleast one modulator for modulating outgoing data from said particularone of stud plurality of origins on an assigned carrier for one of aplurality of upstream channels; at least one second transmitter fortransmitting said modulated assigned carrier from said particular one ofsaid origins; a second converter for converting said assigned carriersin said upstream channels into said output data channels for saidmultiplexed output signal, a noise monitor for monitoring the noiselevel in a particular upstream channel, and equipment for reassigningoutgoing data to a carrier at a different frequency in a differentupstream channel in response to noise level exceeding a predeterminedlevel in said particular upstream channel.
 2. A bidirectionalcommunications system as set forth in claim 1 wherein:said multiplexedinput signal is a standard digital telephony signal.
 3. A bidirectionalcommunications system as set forth in claim 2 wherein:said standarddigital telephony signal includes at least one of the group of a DS-0format signal, a DS-1 format signal, a DS-2 format signal, and a DS-3format signal.
 4. A bidirectional communications system as set forth inclaim 1, wherein:said multiplexed output signal is a standard digitaltelephony signal.
 5. A bidirectional communications system as set forthin claim 4, wherein:said standard digital telephony signal includes atleast one of the group of a DS-0 format signal, a DS-1 format signal, aDS-2 format signal, and a DS-3 format signal.
 6. A bidirectionalcommunications system as set forth in claim 1 wherein:said central pointis the headend of a CATV network; and said origins and destinations ofdata are subscribers of said CATV network.
 7. A bidirectionalcommunications system as set forth in claim 1, wherein:said origins anddestinations of data are subscribers in a tree-type network extendingfrom said central point.
 8. A bidirectional communications system as setforth in claim 7, further comprising:equipment operative for associatingat least one upstream channel with a particular subscriber's telephonyequipment; and equipment for associating at least one downstream channelwith said telephony equipment.
 9. A bidirectional communications systemas set forth in claim 7, further comprising a customer interface unit(CIU) defining a destination for incoming data and an origin foroutgoing data, said CIU including said at least one demodulator, said atleast one modulator, and said at least one second transmitter.
 10. Abidirectional communications system as set forth in claim 1, furthercomprising:equipment for associating a plurality of upstream channelsand a plurality of downstream channels to a single subscriber to providefor selectably variable bandwidth service.
 11. A bidirectionalcommunications system as set forth in claim 10, wherein said selectablyvariable bandwidth service comprises telephony service selected fromsingle line service, multiple line service, ISDN service, and T1service.
 12. An apparatus for the communication of telephony signals toand from a telephony network and to and from a plurality of subscribersof a subscription system including a subscription network having a firstband of frequencies for communicating signals to subscribers in thesubscription network and a second band of frequencies for communicatingsignals from the subscribers, comprising:a telephony network modulatorfor modulating the telephony signals from the telephony network on saidfirst band of said subscription network utilizing a first modulationscheme; a subscriber terminal including a subscriber terminaldemodulator for demodulating the telephony signals in said first bandfrom the subscription network and coupling them to a subscriber; atleast one frequency agile second modulator for modulating telephonysignals from said subscriber in a selected one of a plurality offrequency subbands in said second band of the subscription networkutilizing a second modulation scheme; and a telephony networkdemodulator for demodulating the telephony signals from said second bandof the subscription network and coupling them to the telephony network.13. The apparatus of claim 12, wherein a plurality of said frequencyagile second modulators is operative for modulating telephony signalsfrom the subscriber in a plurality of frequency subbands in said secondband of the subscription network so as to provide selectably variablebandwidth in said second band commensurate with a selected subscribercommunication feature.
 14. The apparatus of claim 13, wherein saidselected subscriber communication feature comprises voice gradetelephone service.
 15. The apparatus of claim 13, wherein said selectedsubscriber communication feature comprises ISDN telephone service. 16.The apparatus of claim 13, wherein said selected subscribercommunication feature comprises plural voice grade telephone service.17. The apparatus of claim 13, wherein said selectably variablebandwidth comprises at least one subband provided in said second band ofsaid subscription network.
 18. The apparatus of claim 17, wherein saidsubband is 128 kHz.
 19. The apparatus of claim 17, wherein saidselectably variable bandwidth comprises a plurality of non contiguous128 kHz subbands.
 20. The apparatus of claim 17, further comprising:anoise monitor for monitoring the noise level in a selected subband insaid second band associated with a selected subscriber, and wherein saidfrequency agile second modulator is operative to reassign signals insaid selected subband to another subband at another frequency inresponse to a determination by said noise monitor that the noise levelin said selected subband exceeds a predetermined level.
 21. Theapparatus of claim 12, wherein said first modulation scheme is QPR, andsaid second modulation scheme is QPSK.
 22. The apparatus of claim 12,further comprising an address and control unit (ACU) for associatingfrequency subbands in said second band of the subscription network withsubscribers.
 23. The apparatus of claim 22, wherein said ACU maintainsan allocation table in memory storing information in associationselected from the group comprising: subscriber identification, frequencysubband, noise level, service level, security status, and line status.24. The apparatus of claim 12, further comprising:a broadcast messageinformation source for generating a telephony message for broadcast to aselected group of subscribers on the subscription network; and a devicefor coupling said broadcast message to a carrier in the forward band ofthe subscription network for communication to said selected group ofsubscribers, whereby a telephony message is generated at a single sourceand delivered to plural subscribers.
 25. The apparatus of claim 12,wherein said first modulation scheme is QPR, and said second modulationscheme is QPSK.
 26. The apparatus of claim 12, further comprising anaddress and control unit (ACU) for associating frequency subbands insaid second band of the subscription network with subscribers.
 27. Amethod of operating a communication system to couple telephony signalsto and from a telephony network and to and from a plurality ofsubscribers of a subscription system including a tree-and-branch typebroadband subscription network extending from a headend to thesubscribers, comprising the steps of:providing a telephony networkinterface for telephony signals from the telephony network to theheadend; providing an interface for telephony signals from a subscriberto a subscriber terminal connected to the subscription network;providing a first band of frequencies for communicating signals tosubscribers from the headend; modulating the telephony signals from thetelephony network on the first band of the subscription networkutilizing a first modulation scheme; providing a second band offrequencies for communicating signals to the headend from subscribers;subdividing the second band of frequencies into a plurality ofselectable subbands; in response to a request for telephony service witha subscriber, selectably allocating a particular one of the selectablesubbands in the second band of frequencies to the subscriber; andmodulating telephony signals from the subscriber in the particularsubband utilizing a second modulation scheme to transmit said telephonysignals from the subscriber to said telephony network interface.
 28. Themethod of claim 27, wherein the second modulation scheme comprises amodulation scheme that is relatively noise-resistant in the upstreamdirection in the tree-and-branch network structure.
 29. The method ofclaim 28, wherein the second modulation scheme is quadrature phase shiftkeying (QPSK).
 30. The method of claim 27, further comprising the stepof allocating one or more selected frequency subbands in the second bandof the subscription network so as to provide selectably variablebandwidth commensurate with a selected subscriber communication feature.31. The method of claim 27, wherein the request for telephony serviceoriginates at a subscriber having a default level of telephony service.32. The method of claim 31, wherein the default level of telephoneservice is DS0 (64 kbps).
 33. The method of claim 27, wherein therequest for telephony service originates at a subscriber having selectedone of a plurality of selectable levels of communications serviceavailable to the subscriber.
 34. The method of claim 33, wherein each ofthe plurality of selectable levels of communications services requires apredetermined data communications bandwidth, and further comprising thestep of selecting a plurality of frequency subbands in the second bandof the subscription network.
 35. The method of claim 34, wherein therequest for telephone service originating at a subscriber comprises arequest selected from: single line telephony service, multiple linetelephony service, ISDN telephony service, data communications service,videoconferencing service, interactive television service, video gameservice, security monitoring service.
 36. The method of claim 33,further comprising the steps of:communicating a request for a selectedservice level to the headend; determining identity of the subscriberrequesting the selected service level: verifying that the subscriber isauthorized to receive the requested service level; in response toverification that the subscriber is authorized to receive the requestedservice level, allocating one or more selected frequency subbands in thesecond band of the subscription network so as to provide selectablyvariable bandwidth commensurate with selected service level;communicating the identify of the one or more selected frequencysubbands to the subscriber; and receiving signals from the subscriber inthe one or more selected frequency subband from the subscriber at theheadend.
 37. The method of claim 27, wherein the request for telephonyservice originates at the headend in response to an incomingcommunication directed to a subscriber, and further comprising thesteps:determining identity of the particular subscriber to receive theincoming communication; determining an appropriate service level toprovide the communication to the particular subscriber; allocating oneor more selected frequency subbands in the second band of thesubscription network so as to provide selectably variable bandwidthcommensurate with determined appropriate service level; communicatingthe identity of the one or more selected frequency subbands to theparticular subscriber; communicating the incoming communication to theparticular subscriber in the first band of frequencies; at thesubscriber terminal associated with the particular subscriber, receivingthe identity of the one or more selected frequency subbands forcommunications back to the headend; and communicating subscriber signalsto the headend in the one or more selected frequency subbands.
 38. Themethod of claim 37, further comprising the steps:receiving signals atthe headend from the particular subscriber in the one or more selectedfrequency subbands; demodulating the signals to obtain standardtelephony signals; routing the standard telephony signals from theparticular subscriber to a communications port associated with theincoming communication directed to the particular subscriber.
 39. Themethod of claim 38, further comprising the steps:multiplexing aplurality of standard telephony signals obtained from a plurality ofsubscribers into a standard multiplexer telephony signal.
 40. The methodof claim 39, wherein the standard telephony signal is a DS0 format, andwherein the standard multiplexed telephony signals are selected fromformats DS1, DS2, DS3, E1, T1, and SONET.
 41. A method of operating abidirectional communication system to couple telephony signals to andfrom a telephony network and to and from a plurality of subscribers of asubscription system including a broadband subscription network extendingfrom a headend to the subscribers, each subscriber having a subscriberterminal, comprising the steps of:receiving a multiplexed telephonysignal containing a plurality of predetermined telephony signals in aplurality of telephony channels; demultiplexing the multiplexedtelephony signal to obtain a particular telephony signal from aparticular telephony channel; communicating the particular telephonysignal from the headend to a particular subscriber at a subscriberdestination associated with the particular subscriber in a firstfrequency band in the subscription system; selecting a particularsubband in a second frequency band in the subscription system to receivesubscriber telephony signals from the particular subscriber;communicating the identity of the selected particular subband in thesecond frequency band to the particular subscriber from the headend soas to cause a subscriber terminal to transmit the subscriber's telephonysignals in the selected subband: communicating subscriber telephonysignals from the particular subscriber at the subscriber destination tothe headend in the selected particular subband; and coupling thesubscriber telephony signals to the particular telephony channel. 42.The method of claim 41, wherein the multiplexed telephony signalcomprises a SONET signal.
 43. The method of claim 41, wherein themultiplexed telephony signal is communicated via an optical fiber linkfrom a telephony central office to the headend.
 44. The method of claim41, wherein the multiplexed telephony signal is communicated from atelephony central office to the headend, and thence via an optical fiberlink from the headend to a fiber node.
 45. The method of claim 41,wherein the step of communicating the identity of the selectedparticular subband in the second frequency band to the particularsubscriber comprises the step of providing a signaling channel forcommunication of status signals between a subscriber and the headend.46. The method of claim 41, further comprising the step of changing thefrequency from the selected subband in the second frequency band toanother frequency subband during a communication session involving theparticular subscriber.
 47. The method of claim 46, further comprisingthe step of monitoring the noise level in the selected subband, andwherein the step of changing the frequency of the selected subband iscarried out in response to a determination in the monitoring step thatthe noise level in the selected subband exceeds a predeterminedthreshold.
 48. The method of claim 47, wherein the subscriber telephonysignals are digital signals transmitted in a plurality of packets ofdigital data, and wherein the step of monitoring the noise level in theselected subband comprises the steps:determining a cyclic redundancycheck (CRC) value for each packet of digital data comprising thesubscriber telephony signal prior to transmission of the signal;receiving the CRC value at the headend; in response to a determinationthat the CRC value is incorrect, incrementing an error count register;comparing the error count register to a predetermined value; when theerror count register exceeds a predetermined threshold value, setting anoisy channel status flag; and changing the frequency in response tosetting the noisy channel status flag.
 49. The method of claim 48,wherein the step of comparing the error count register to thepredetermined threshold value is carried out on a periodic basis so asto determine the number of transmission errors associated with apredetermined number of packets transmitted in a predetermined time. 50.A telephony system for communicating telephony signals between atelephony network and a broadband communication network including aheadend communicating to a plurality of subscribers, comprising:amodulator, coupled between the telephony network and the headend, formodulating the telephony signals from the telephony network on a carrierin a first band of the broadband communication network; equipment fordetermining a selected service level for a particular subscriber and forcommunicating information for effecting the selected service levelindicating one or more selected frequency subbands in a second band ofthe broadband communication network to the particular selectedsubscriber; and a demodulator, coupled between the telephony network andthe headend, for demodulating the telephony signals from the particularsubscriber in the one or more selected frequency subbands and couplingthem to the telephony network.
 51. The system of claim 50, wherein thebroadband communication network includes a subscriber terminal fordemodulating the telephony signals in the first band of broadbandnetwork and coupling them to the subscriber, and for modulating thetelephony signals from the subscriber in the one or more selectedfrequency subbands in the second band of the broadband network forcommunication to the headend.
 52. The system of claim 51, wherein thesubscriber terminal includes a frequency agile modulator for modulatingthe telephony signals in the one or more selected frequency subband inthe second band, and further comprising:a noise monitor for monitoringthe noise level in a selected frequency subband associated with aparticular subscriber, and equipment responsive to the noise monitor forcommunicating a frequency change signal to a particular subscriber whenthe noise level in the selected frequency subband exceeds apredetermined threshold, whereby the subscriber terminal changes thefrequency for communicating at least some of the telephony signals to adifferent selected frequency subband when a given channel becomes toonoisy.
 53. The system of claim 50, wherein the broadband communicationnetwork is a cable television (CATV) network, and further comprisingequipment for providing television program signals in said first band offrequencies to subscribers.
 54. The system of claim 50, wherein theequipment for determining the selected service level comprises:equipmentfor communicating in the first band a directory message in a directorychannel containing subscriber identification information and theidentity of one or more selected frequency subbands in the second bandassociated with the subscriber identification information.
 55. Thesystem of claim 50, wherein the information for effecting the selectedservice level comprises a message including address informationcorresponding to a selected subscriber and frequency subband informationcorresponding to the one or more selected frequency subbands.
 56. Thesystem of claim 55, wherein said channel assignment message istransmitted in a directory channel.
 57. The system of claim 50, furthercomprising:a frequency agile modulator located at the subscriberoperative to change the frequency at which telephony signals are beingcommunicated to the headend from a first frequency subband to a secondfrequency subband in response to a command received from the headend.58. The system of claim 57, wherein the frequency agile modulatorcomprises a quadrature phase shift keying (QPSK) modulator operative atselectable carrier frequencies varying in discrete increments of 128 kHzchannels, beginning at a nominal initial carrier frequency of 5.12 MHz,with a nominal data rate of 144 kbps per channel.
 59. The system ofclaim 58, wherein each said 144 kbps channel comprises two 64 kbps DS0telephony () channels and one 16 kbps overhead channel including dataheaders, address information, and CRC data.
 60. The system of claim 58,wherein each 128 kHz channel comprises a 108 kHz bandwidth data channeland 20 kHz in guard bands.
 61. The system of claim 50, wherein telephonysignals from the headend communicated to the subscriber are transmittedin said first frequency band as downstream signals, and furthercomprising:a customer interface unit including a demodulator fordemodulating said downstream signals in the first frequency band toobtain an incoming telephony signal and coupling said incoming telephonysignal to a telephony port.
 62. The system of claim 61, wherein saiddownstream signals are communicated to the customer interface unit viaQPR modulation.
 63. The system of claim 61, wherein said downstreamsignals communicated in the first frequency band comprise:a plurality ofincoming telephony signals arranged in a plurality of channels; at leastone directory channel containing said second signals; and at least onesignaling channel containing status information.
 64. The system of claim63, wherein the downstream signals comprise a 3.168 MHz QPR modulatedsignaling containing 96 DS0 digital incoming telephony signals, saiddirectory channel, said signaling channel, and CRC data associated witha frame of digital signals.
 65. A customer interface unit for connectionto a broadband communication network, the customer interface unitoperative for receiving first signals in a first frequency band from aheadend associated with the broadband communication network, forreceiving second signals from the headend, and for communicatingtelephony signals between a subscriber and the headend, said customerinterface unit comprising:a first demodulator for demodulating firstsignals in the first frequency band and for coupling them to an outputport of the customer interface unit; a second demodulator for receivingsecond signals and for identifying, from said second signals, one of aplurality of frequency subbands in a second band of frequencies in thebroadband communication network for communicating telephony signals tothe headend; and a frequency agile modulator responsive to theidentified one of said plurality of frequency subbands in the secondband of frequencies for modulating the telephony signals from thecustomer interface unit in the identified frequency subband.
 66. Thecustomer interface unit of claim 65, wherein the broadband communicationnetwork is a cable television (CATV) network.
 67. The customer interfaceunit of claim 66, wherein said first signals comprise television programsignals, and wherein said output port comprises a video signal port forconnection to a CATV set top converter.
 68. The customer interface unitof claim 65, wherein said output port comprises a telephony port forreceiving the telephony signals into the customer interface unit. 69.The customer interface unit claim 65, wherein said output portcomprises:a video signal output port for coupling to a cable televisionset top terminal; and at least one telephony signal port for coupling toa subscriber's home telephony network.
 70. The customer interface unitof claim 69, further comprising:a subscriber input port for receivingsubscriber signals associated with an interactive consumer deviceselected from: pay per view television, interactive television, videogames, and shopping channel television selection.
 71. The customerinterface unit of claim 65, wherein the second signals are communicatedin the first frequency band.
 72. The customer interface unit of claim65, wherein the second signals comprise a message including addressinformation corresponding to a selected subscriber and frequency subbandinformation corresponding to the one or more selected frequencysubbands.
 73. The customer interface unit of claim 65, wherein saidsecond signals are transmitted in a directory channel.
 74. The customerinterface unit of claim 65, wherein said frequency agile modulator isoperative to change the frequency at which telephony signals are beingcommunicated to the headend from a first frequency subband to a secondfrequency subband in response to a command received as the secondsignal.
 75. The customer interface unit of claim 65, wherein saidfrequency agile modulator comprises a quadrature phase shift keying(QPSK) modulator operative at selectable carrier frequencies varying indiscrete increments of 128 kHz channels, beginning at a nominal initialcarrier frequency of 5.12 MHz, with a nominal data rate of 144 kbps perchannel.
 76. The customer interface unit of claim 75, wherein each said144 kbps channel comprises two 64 kbps DS0 telephony channels and one 16kbps overhead channel including data headers, address information, andCRC data.
 77. The customer interface unit of claim 75, wherein each 128kHz channel comprises a 108 kHz bandwidth data channel and 20 kHz inguard bands.
 78. The customer interface unit of claim 65, whereintelephony signals from the headend communicated to the subscriber arealso transmitted in said first frequency band as downstream signals,wherein said customer interface unit further comprises:a thirddemodulator for demodulating said downstream signals in the firstfrequency band to obtain an incoming telephony signal and coupling saidincoming telephony signal to a telephony port.
 79. The customerinterface unit of claim 78, wherein said downstream signals arecommunicated to the customer interface unit via QPR modulation.
 80. Thecustomer interface unit of claim 78, wherein said downstream signalscommunicated in the first frequency band comprise:a plurality ofincoming telephony signals arranged in a plurality of channels; at leastone directory channel containing said second signals; and at least onesignaling channel containing status information.
 81. The customerinterface unit of claim 80, wherein the downstream signals comprise a3.168 MHz QPR modulated signaling containing 96 DS0 digital incomingtelephony signals, said directory channel, said signaling channel, andCRC data associated with a frame of digital signals.
 82. A method ofoperating a broadband communication network, including a telephonynetwork interface for connection to a telephony network, forcommunicating signals between subscribers and the telephony network,comprising the steps of:receiving a multiplexed incoming telephonysignal from the telephony network comprising a plurality of telephonysignals provided in a standard multiplexed telephony format;demultiplexing the incoming multiplexed telephony signal to obtain atleast one selected incoming telephony signal intended for a particularsubscriber on the broadband communication network; transmitting theselected incoming telephony signal to the particular subscriber in afirst frequency band on the broadband communication network utilizing afirst modulation scheme; receiving the selected incoming telephonysignal at a customer interface unit connected to the broadbandcommunication network associated with the particular subscriber;coupling the selected incoming telephony signal transmitted via thefirst modulation scheme to a telephony port associated with the customerinterface unit; receiving outgoing telephony signals from a subscriberat the telephony port; transmitting the outgoing telephony signals on atleast one assigned carrier in a selected subband in a second frequencyband on the broadband communication network utilizing a secondmodulation scheme; demodulating the outgoing telephony signalstransmitted via the second modulation scheme in the selected subband toobtain an outgoing telephony signal associated with the particularsubscriber; multiplexing the outgoing telephony signal from theparticular subscriber with other telephony signals associated with othersubscribers to obtain a multiplexed outgoing telephony signal comprisinga plurality of telephony signals in a standard multiplexed telephonyformat to telephony network; and coupling the multiplexed outgoingtelephony signal to the telephony network.
 83. The method of claim 82,wherein the second modulation scheme is quadrature phase shift keying(QPSK).
 84. The method of claim 82, further comprising the stepof:allocating one or more selected frequency subbands in the secondfrequency band on the broadband communication network so as to provideselectably variable bandwidth service.
 85. The method of claim 84,wherein said selectably variable bandwidth service comprises telephonyservice selected from a single line service, multiple line service, ISDNservice and T1 service.
 86. The method of claim 82, wherein themultiplexed incoming telephony signal comprises a SONET signal.
 87. Themethod of claim 82, wherein the multiplexed incoming telephony signal iscommunicated via an optical fiber link from a telephony central officeto a headend of the broadband communication network.
 88. The method ofclaim 82, wherein the multiplexed incoming signal is communicated from atelephony central office to a headend of the broadband communicationnetwork, and thereafter is communicated via an optical fiber link fromthe headend to a fiber node.
 89. The method of claim 82, wherein themultiplexed outgoing telephony signal is communicated via an opticalfiber link from a headend of the broadband communications network to atelephony central office.
 90. The method of claim 82, wherein themultiplexed outgoing signal is communicated via an optical fiber linkfrom a fiber node to a headend of the broadband communication network,and thereafter is communicated from the headend to a telephony centraloffice.
 91. The method of claim 82, further comprising the stepof:changing the frequency from the selected subband in the secondfrequency band on the broadband communication network to anotherfrequency subband during a communication session.
 92. The method ofclaim 91, further comprising the step of:monitoring the noise level inthe selected subband, and wherein said step of changing the frequency ofthe selected subband is carried out in response to a determination insaid monitoring step that the noise level in the selected subbandexceeds a predetermined threshold.
 93. The method of claim 92, whereinsaid step of monitoring the noise level in the selected subbandcomprises the steps of:determining a cyclic redundancy check (CRC) valuefor each packet of digital data comprising the telephony signal prior totransmission of the signal; receiving the CRC value at the headend; inresponse to a determination that the CRC value is incorrect,incrementing an error count register; comparing the error count registerto a predetermined value; when the error count register exceeds apredetermined threshold value, setting a noisy channel status flag; andchanging the frequency in response to setting the noisy channel statusflag.
 94. The method of claim 93, wherein the step of comparing theerror count register to the predetermined threshold value is carried outon a periodic basis so as to determine the number of transmission errorsassociated with a predetermined number of packets transmitted in apredetermined time.
 95. A method of operating a bidirectionalcommunication system to couple telephony signals to and from a telephonynetwork and to and from a plurality of subscribers of a subscriptionsystem including a broadband subscription network extending from aheadend to the subscribers, comprising the steps of:receiving amultiplexed telephony signal containing a plurality of predeterminedtelephony signals in a plurality of telephony channels; demultiplexingthe multiplexed telephony signal to obtain a particular telephony signalfrom a particular telephony channel; communicating the particulartelephony signal from the headend to a particular subscriber at asubscriber destination associated with the particular subscriber in afirst frequency band in the subscription system; selecting a particularsubband in a second frequency band in the subscription system to receivesubscriber telephony signals from the particular subscriber;communicating subscriber telephony signals from the particularsubscriber at the subscriber destination to the headend in the selectedparticular subband; and coupling the subscriber telephony signals to theparticular telephony channel; and changing the frequency from theselected subband in the second frequency band to another frequencysubband during a communication session involving the particularsubscriber.
 96. The method of claim 95, further comprising the step ofcommunicating the identity of the selected subband in the secondfrequency band to the particular subscriber from the headend so as tocause the subscriber terminal to transmit the subscriber's telephonysignals in the selected subband.
 97. The method of claim 96, wherein thestep of communicating the identity of the selected subband in the secondfrequency band to the particular subscriber comprises the step ofproviding a signaling channel for communication of status signalsbetween a subscriber and the headend.
 98. The method of claim 95,further comprising the step of monitoring the noise level in theselected subband, and wherein the step of changing the frequency of theselected subband is carried out in response to a determination in themonitoring step that the noise level in the selected subband exceeds apredetermined threshold.
 99. An apparatus for the communication oftelephony signals to and from a telephony network and to and from aplurality of subscribers of a subscription system including asubscription network having a first band of frequencies forcommunicating signals to subscribers in the subscription network and asecond band of frequencies for communicating signals from thesubscribers, comprising:a telephony network modulator for modulating thetelephony signals from the telephony network on said first band of saidsubscription network utilizing a first modulation scheme; a subscriberterminal including a subscriber terminal demodulator for demodulatingthe telephony signals in said first band from the subscription networkand coupling them to a subscriber; a plurality of frequency agile secondmodulators for modulating telephony signals from said subscriber in aplurality of frequency subbands in said second band of the subscriptionnetwork utilizing a second modulation scheme so as to provide selectablyvariable bandwidth in said second band commensurate with a selectedsubscriber communication feature; and a telephony network demodulatorfor demodulating the telephony signals from said second band of thesubscription network and coupling them to the telephony network. 100.The apparatus of claim 99, wherein said selected subscribercommunication feature comprises voice grade telephone service.
 101. Theapparatus of claim 99, wherein said selected subscriber communicationfeature comprises ISDN telephone service.
 102. The apparatus of claim99, wherein said selected subscriber communication feature comprisesplural voice grade telephone service.
 103. The apparatus of claim 99,wherein said selectably variable bandwidth comprises at least onesubband provided in said second band of said subscription network. 104.The apparatus of claim 103, wherein said selectably variable bandwidthcomprises a plurality of non contiguous subbands.
 105. The apparatus ofclaim 103, further comprising:a noise monitor for monitoring the noiselevel in a selected subband in said second band associated with aselected subscriber, and wherein said frequency agile second modulatorsare operative to reassign signals in said selected subband to anothersubband at another frequency in response to a determination by saidnoise monitor that the noise level in said selected subband exceeds apredetermined level.
 106. An apparatus for the communication oftelephony signals to and from a telephony network and to and from aplurality of subscribers of a subscription system including asubscription network having a first band of frequencies forcommunicating signals to subscribers in the subscription network and asecond band of frequencies for communicating signals from thesubscribers, comprising:a telephony network modulator for modulating thetelephony signals from the telephony network on said first band of saidsubscription network utilizing a first modulation scheme; a subscriberterminal including a subscriber terminal demodulator for demodulatingthe telephony signals in said first band from the subscription networkand coupling them to a subscriber; at least one frequency agile secondmodulator for modulating telephony signals from said subscriber in aselected one of a plurality of frequency subbands in said second band ofthe subscription network utilizing a second modulation scheme; atelephony network demodulator for demodulating the telephony signalsfrom said second band of the subscription network and coupling them tothe telephony network; and an address and control unit (ACU) forassociating frequency subbands in said second band of the subscriptionnetwork with subscribers, said ACU maintaining an allocation table in amemory storing information in association selected from the groupcomprising: subscriber identification, frequency subband, noise level,service level, security status, and line status.
 107. The apparatus ofclaim 106, wherein a plurality of said frequency agile second modulatorsis operative for modulating telephony signals from the subscriber in aplurality of frequency subbands in said second band of the subscriptionnetwork so as to provide selectably variable bandwidth in said secondband commensurate with a selected subscriber communication feature. 108.The apparatus of claim 107, wherein said selected subscribercommunication feature comprises voice grade telephone service.
 109. Theapparatus of claim 107, wherein said selected subscriber communicationfeature comprises ISDN telephone service.
 110. The apparatus of claim107, wherein said selected subscriber communication feature comprisesplural voice grade telephone service.
 111. The apparatus of claim 107,wherein said selectably variable bandwidth comprises at least onesubband provided in said second band of said subscription network. 112.The apparatus of claim 111, wherein said selectably variable bandwidthcomprises a plurality of non contiguous subbands.
 113. The apparatus ofclaim 111, further comprising:a noise monitor for monitoring the noiselevel in a selected subband in said second band associated with aselected subscriber, and wherein said frequency agile second modulatoris operative to reassign signals in said selected subband to anothersubband at another frequency in response to a determination by saidnoise monitor that the noise level in said selected subband exceeds apredetermined level.